MEMCAL    SCHOOL 


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tlG.    1. 

Convex  Surface  of  Cerebrum  Cortical  Areas. 


Fig.  II. 
Cortical  Areas  on  Medial  Surface  of  Cerebrum. 


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ANATOMY 

OF   THE 


Brain  AND  Spinal  Cord 

WITH    SPECIAL    REFERENCE    TO 

THE  GROUPING  AND   CHAINING  OF  NEURONES 
INTO  CONDUCTION  PATHS. 

For  Students  and  Practitioners. 


HARRIS    E.^SANTEE,  M.  D.,  Ph.  D., 

Professor  of  Anatomy  in  the  College  of  Physicians  and  Surgeons, 

Medical  Department,  University  of  Illinois;  Professor  of 

Anatomy  in  Harvey  Medical  College,  Chicago. 

WITH   A   PREFACE   BY 

WILLIAM   T.  ECKLEY,  M.  D., 

Professor  of  Anatomy  in  the  Medical  and  Dental  Departments, 
University  of  Illinois. 


THIRD    EDITION 
REVISED   AND    ENLARGED. 


Chicago  : 

E.  H.  COLEGROVE. 

1903. 


Copyright,  1903,  by  Harris  E.  Santee 
Chicago,  III. 


Q  HA4  5 


%-J 


A 


PEEFACE. 

It  is  with  pleasure  I  respond  to  the  author's  invitation  to 
write  an  introductory  page,  and  I  sincerely  acknowledge  the 
compliment. 

My  remarks,  necessarily  few,  are  in  the  nature  of  convic- 
tions founded  on  a  study  of  this  and  the  previous  edition,  on 
a  comparison  of  this  work  with  others  of  similar  nature,  on 
a  long  personal  acquaintance  with  the  author,  an  appreciation 
of  his  conception  of  anatomy  and  his  methods  of  teaching 
the  same.  To  peruse  the  book,  is  to  convince  one  of  its  value 
as  a  contribution  to  our  literature;  to  know  the  author,  is  to 
enhance  the  desirability  of  the  book. 

It  is  needless  to  comment  on  detail,  logical  arrangement 
and  orderly  subordination  of  minor  to  major  parts,  looking 
to  the  ultimate  desideratum  of  a  mionograph  on  the  brain  and 
spinal  cord,  for  the  use  of  students  and  practitioners.  Such 
features  are  possessed  by  books  in  general.  My  remarks  will 
be  directed  to  what  I  consider  superior  qualities,  these  inci- 
dentals which  relieve  the  tedium  of  scientific  detail  and  in- 
delibly impress  the  practical  value  of  a  subject. 

The  composition,  relation  and  contour  of  the  operculum 
and  posterior  part  of  the  inferior  frontal  gyrus,  become  more 
interesting,  when  it  is  shown  that  "They  constitute  the  re-' 
gion  of  speech.''  In  like  manner,  that  "The  temporal  lobe 
is  the  probable  seat  of  the  centers  of  taste,  smell  and  hear- 
ing," and  that  "The  ascending  frontal,  ascending  parietal 
and  superior  parietal  convolutions  are  the  best  known  motor 
areas  of  the  cortex,"  are  physiological  observations  which 

III 


5240.') 


PREFACE. 

instruct  and  fascinate  alike.  In  this  manner,  throughout 
the  book,  the  author  invokes  function  of  a  region  to  gain  an 
anatomical  end. 

The  olfactory  lobe  in  man,  represented  by  the  bulb,  tract, 
trigone,  area  of  Broca  and  anterior  perforated  space,  finds 
the  lobar  antecedent  and  a  reason  for  its  name,  in  the  lower 
animals,  and  in  this  way  the  author  elucidates  a  point  which 
were  incomprehensible  to  the  student  without  such  compari- 
son. 

The  adult  human  brain  is  complex,  stable,  coherent  and 
heterogeneous,  but  as  a  simple,  comprehensible  means  to  a 
great  teaching  expedient,  the  author  invokes  the  precepts  of 
embryology  to  show  that  this  composite  brain  had  a  simple 
vesicular  prototype  whose  simple  cavity  became  complex  ven- 
tricles, whose  simple  spongioblasts  became  complex  neu- 
rogliar  network,  whose  simple  primitive  neuroblasts  became 
neurones,  with  cell-bodies  and  dendrites  in  cortex  and  ganglia, 
and  medullated  axones  forming  the  white  substance  of  the 
brain. 

Numerous  illustrations  might  be  drawn  from  every  chap- 
ter of  the  book  to  show  like  superior  teaching  qualities,  but 
observations  which  even  the  most  casual  perusal  of  the  book 
itself  makes  apparent  add  nothing  of  value  to  criticism. 

In  his  presentation  of  the  tracing  of  impulses,  Dr.  Santee 
has  done  more  to  simplify  the  complex  conduction  paths  to 
and  from  the  brain  than  any  author  after  whom  I  have  read. 
'In  this  respect  his  book  excels,  and  must  appeal  to  teachers 
of  anatomy,  practitioners  of  medicine  and  students  alike. 

The  conception  of  a  motor  nerve  according  to  many  is  a 
tangible  band  of  white  matter  (as  the  anterior  tibial)  asso- 
ciated above  with  a  plexus.  Dr.  Santee's  conception,  how- 
ever, is  a  path  composed  of  numerous  neurones  extending 

IV 


PREFACE. 

from  a  cortical  area  in  the  neighborhood  of  the  Rolandic 
fissure  through  the  pyramidal  tracts  of  the  spinal  cord  to  both 
co-ordinated  and  inco-ordinated  muscles.  His  conception  of 
a  sensory  conduction  path  is  not  the  ordinary  one  which 
leaves  the  student  in  doubt  as  to  the  location  of  trophic  cells 
of  centripetal  nerves^  but  the  embryological  one  which  recog- 
nizes sensory  spinal  and  sensory  cranial  nerves  as  growing 
toward  and  into  the  brain,  from  posterior  root  and  cephalic 
ganglia  respectively.  Such  a  conception  of  motor  and  sen- 
sory nerves  enables  a  student  to  read  intelligently  the  de- 
generations. Again,  it  is  superior  teaching  that  ascribes 
function  to  the  definite  tracts  of  fibers,  to- wit :  "The  pyram- 
idal tracts  are  motor;"  "Gower's  tract  probably  carries 
thermic  and  pathetic  impulses;"  "GolFs  column  carries  im- 
pulses of  the  muscular  sense;"  "All  varieties  of  impulse  are 
carried  by  Burdach's  column;"  "The  direct  cerebellar  tract 
conveys  impulses  of  equilibrium  received  especially  from  the 
viscera." 

In  conclusion,  Dr.  Santee's  "Anatomy  of  the  Brain  and 
Spinal  Cord"  is  concise,  exact,  scholarly,  and  possesses  su- 
perior qualities  in  the  manner  of  elucidation;  it  gives  the 
most  comprehensive  exposition  of  the  conduction  paths  of 
the  brain  and  spinal  cord  of  any  book  in  our  language,  and 
is  destined  to  become  popular  everywhere. 

Very  truly, 

W.  T.  ECKLEY. 


CONTENTS. 
Chapter  I. 

PAGE. 

Membranes  of  the  Brain 1-6 

Dura  Mater 1-4 

Middle  meningeal  artery 3 

Arachnoid 4-5 

Pia  mater 5-6 

Table  1.     Grand  divisions  of  brain 6-7 

Chapter  II. 

The   Cerebrum. 8-51 

Section  i. 

Exterior  surface 9-24 

Convex  surface 9-14 

Fissures 9-11 

Lobes  and  convolutions 11-14 

Medial  and  tentorial  surface 14-17 

Fissures 14-16 

Lobes  and  convolutions 16-17 

Basal  surface 17-24 

Medial  structures 18-21 

Lamina  cinerea ,  18 

Tuber  cinereum 18 

Pituitary  body 19 

Corpora  albicantia 19 

Optic  commissure 20 

Lateral  structures 21-24 

Orbital  lobe 21 

Island  of  Reil 22 

Olfactory  lobe 22 

Section  2.. 

Interior  surface  of  cerebrum 24-51 

Internal  capsule , 25-28 

VII 


CONTENTS. 

PAGE. 

Corpus  callosum 28-30 

General  cavity  of  cerebrum 30-31 

Fornix 32-33 

Septum  lucidum 33 

Fifth  ventricle 33-34 

Lateral  ventricle,  body  34-42 

Corpus .  striatum 35-37 

Taenia  semicircularis 37 

Optic  thalamus 37 

Choroid  plexus 38 

Cornua,  anterior,  posterior  and  middle 38-42 

Third  ventricle 42-43 

Boundaries 43-44 

Roof  epithelium 44-45 

Pineal  body 45-46 

Velum  interpositum 46-47 

Choroid  plexus  and  tela 46 

Anterior  commissure 47 

•  ;  Optic  thalamus 48-50 

Hypothalamic  region 50 

Geniculate  bodies,  external  and  internal 50-51 

Chapter   III. 

The  Mid  Brain 52-65 

Surfaces 52-54 

Interior 54-65 

Crustae 54-56 

J                  Intermediate  bundle 55 

Temporal  cerebro-corticopontal  tract 55 

Pyramidal  tract 55-56 

Frontal  cerebro-corticopontal  tract 56 

Substantia  nigra 56-57 

Tegmentum 57-65 

Aqueduct  of   Sylvius 58 

Corpora  quadrigemina 59 

Internal  geniculate  body 60 

Fibers  of  tegmentum 60-65 

Posterior  longitudinal  bundle 61 


CONTENTS. 

PAGE. 

Anterior  longitudinal  bundle 62 

Fillet  or  lemniscus 6^-63 

Superior  peduncle  of  cerebellum 64 

Olivary  bundle 64 

Tract  from  red  nucleus 65 

Chapter  IV. 

Gray  and  White  Matter  of  Cerebrum  and  Mid  Brain..  66-99 

Neurone 66-70 

Sustentacular  tissue 67 

Cortical  gray  matter 70-76 

Motor  areas 70-71 

Somaesthetic  area  (common  sensory) 70 

Special  sense  areas 71 

Association  centers 71-72 

Effect  of  lesions  in  special  areas 72 

Layers  of  typical  cerebral  cortex 72-74 

Exceptions    74-76 

Ganglionar  gray  matter 76-84 

Corpus  striatum 76-78 

Caudate  nucleus 76 

Lenticular  nucleus 76 

Lesions  in  corpus  striatum 77 

Optic  thalamus 78-81 

Nuclei  of  thalamus 78-79 

White  matter  of  thalamus 79-80 

Lesions  of  lateral  nucleus  and  nucleus  of  pulvinar  78 

Nucleus  hypothalamicus  (Luysi) 81 

Nucleus  ruber  (red  nucleus) 81 

Geniculate  bodies 82 

Corpora  quadrigemina 82-83 

Substantia  nigra 83-84 

Central,  or  ventricular,  gray  matter 84-85 

Lamina  cinerea  and  tuber  cinereum 84 

Middle  commissure  (massa  intermedia) 84 

Nuclei  of  oculomotor  and  trochtear  nerves 84 

Projection  fibers — Motor. 85-89 

Internal  capsule  and  crusta 85-89 

IX 


CONTENTS. 

PAGE, 

Pyramidal  tract 86-89 

Cranial  fibers 87 

Upper  extremity  fibers 87 

Trunk  fibers 88 

Lower  extremity  fibers 88 

Frontal  cerebro-corticopontal  tract 86 

Temporal  cerebro-corticopontal  tract 86 

Intermediate  bundle 86 

Tegmentum 88 

Descending  tract  from  red  nucleus 88 

Anterior  longitudinal  bundle 88 

Lesions  of  motor  tracts 89 

Projection  fibers — Sensory 89-91 

Tegmentum 89 

Internal  capsule — common  sensations 89-91 

Three  systems  of  Flechsig,  or  cortical  fillet 89-90 

Ansa  peduncularis 89 

Ansa  lenticularis 89-90 

Anterior  stalk  of  thalamus 90 

Lesions  of  cortical  fillet 90 

Internal  capsule — special  sensations 90-91 

Acustic  radiations 90 

Optic  radiations 90-91 

Lesions  of  acustic  and  optic  radiations 90-91 

Commissural  fibers 91 

Corpus  callosum 91 

Anterior  commissure 91 

Lyre,  or  commissura  hippocampi 91 

Association  fibers 91-94 

Short 91 

Certain  lesions  of 92 

Long 92-94 

Cingulum 92 

Fornix.. 92 

Uncinate   fasciculus 93 

Lesion  of , 93 

Superior  longitudinal  fasciculus 93 

Interruption  of 93 

X 


CONTENTS. 

PAGE. 

Inferior  longitudinal  fasciculus 93 

Fasciculus  occipito-frontalis 93 

Perpendicular  fasciculus 94 

Blood  supply  of  cerebrum  and  mid-brain 94-99 

Cortical  system  of  arteries 95-96 

Ganglionar  system  of  arteries 96-97 

Veins 98 

Lymph  spaces 99 

Chapter  V. 
Hind  Brain 100-128 

Section  i. 

Cerebellum 100-118 

Functions 100 

Hemispheres  and  vermis 100-101 

Medullary  vela 101-102 

Cerebellar  peduncles 101-103 

Superior   surface 103-107 

Fissures  and  lobes 103-107 

Inferior  surface 107-111 

Fissures  and  lobes 107-111 

Interior 111-118 

Gray   matter 111-114 

Cortical 111-113 

Functions  and  lesions  of 113 

Ganglionar 113-114 

White  matter 114-118 

Projection  fibers 114-116 

Cerebellar  peduncles 114-116 

Commissural  fibers 116 

Association  fibers 117 

Blood  supply 117-118 

Section  2. 

Pons 118-128 

Surfaces '. 119-120 

White  matter  of  Pons 120-125 

XI 


CONTENTS. 

PAGE 

Transverse  fibers 121-122 

Ventral 121 

Middle 121 

Dorsal 121-122 

Longitudinal  fibers 122-125 

Ventral  (pyramidal) 122 

Middle  (formatio  reticularis) 123 

Fillets 123-124 

Posterior  longitudinal  bundle 124 

Anterior  longitudinal  bundle 124 

Olivary  bundle 124-125 

Tract  from  red  nucleus 125 

Root  of  trifacial  nerve 125 

Dorsal  longitudinal  fibers 125 

Superior  cerebellar  peduncles 125 

Valve  of  Vieussens 125 

Gray  matter  of  pons 126 

Nuclei  pontis 126 

Nuclei  of  formatio  reticularis 126 

Cranial  nerve  nuclei 126 

Superior  olivary  nucleus 126 

Lesions  of  pons 127 

Blood  supply  of  pons 127 

Chapter  VL 

Medulla  Oblongata 128-149 

Surfaces 129-133 

Ventral 130-131 

Lateral 131-132 

Dorsal 132-133 

Interior — white  matter 133-145 

Formatio  reticularis  and  raphe ; 134-135 

Transverse  fibers 135-136 

External    arciform  anterior  and  posterior 135 

Internal  arciform 136 

Sensory,  or  fillet,  decussation 136 

Cerebello-olivary  tract 136 

Dorso-ventral   fibers — nerve  roots 136-137 

XII 


CONTENTS. 

PAGE. 

Longitudinal  fibers 137-145 

Pyramids 138 

Formatio  reticularis  alba 138-139 

Interolivary  fillet 139 

Posterior  and  anterior  longitudinal  bundles.  .139-140 

Formatio  reticularis  grisea 140-141 

Antero-lateral  ground  bundle 141 

Triangular  tract  (Helwig) 141 

Antero-lateral  cerebellar  tracts 141-142 

Tract  from  red  nucleus 142 

Fasciculus  gracilis 142-143 

Fasciculus  cuneatus 142-143 

Fasciculus  Rolandi 143-144 

Direct  cerebellar  tract 144 

Restiform  body 144-145 

Fasciculus  solitarius 145 

Fasciculus  teres 145 

Interior — gray  matter 146-149 

From  anterior  horn 146-147 

From  posterior  horn 147 

Added  nuclei 147  149 

Lesions  of  medulla 149 

Chapter  VI  L 

Fourth  Ventricle 150-158 

Boundaries 150-153 

Eminentia  teres 151-152 

Fovea  superior 151-152 

Locus  coeruleus 151-152 

Trigonum  hypoglossi 152 

Trigonum  vagi 152-153 

Trigonum  acustici ....    152-153 

Table  1 1 .    Origins  of  cranial  nerves 153-158 

Ventral   nuclei,  motor 156-157 

Dorsal  nuclei,  sensory .^ 157-158 

Blood  supply  of  medulla  oblongata 158 

Chapter  VIII. 

Meninges  of  Spinal  Cord 159-161 

Dura  mater 159 

XIII 


CONTENTS. 

PAGE. 

Arachnoid 160 

Pia  mater 160-161 

Ligamentum  denticulatum 161 

Nerve  and  blood  supply 161 

Chapter  IX. 

The  Spinal  Cord ...162-184 

Enlargements  of  cord 163 

Ventricle  of  cord = 163 

Surface 163-165 

Fissures 163-165 

Gray  matter  of  cord 165-171 

Substantia  gelatinosa 166 

Substantia  spongiosa 166 

Anterior  horn  of  crescent 166-168 

Lesions  of 167-168 

Center  of  crescent 168-169 

Posterior  horn  of  crescent 169-170 

Gray  commissure  of  cord 170-171 

White  matter  of  cord 171-182 

Anterior  commissure 171-172 

Nerve  roots 179-182 

Tracts  (longitudinal) 172-179 

Ascending 172 

Descending 172 

Mixed  (ascending  and  descending) 173 

Antero-lateral  ground  bundle 173-174 

Anterior  and  posterior  longitudinal  bundles.  .173-174 

Uncrossed  (direct )  pyramidal 174 

Antero-lateral  descending  cerebellar 174 

Antero-lateral  ascendmg  cerebellar 175 

Triangular  (Helwig)  olivary  of  cord 175 

Direct  cerebellar. . 175-176 

Crossed  pyramidal 176-177 

Crossed  descending  from  red  nucleus 176 

Lesions  of  pyramidal  tracts 177 

Marginal  (Lissauer) 177 

Postero-lateral  (Burdach) 177-178 

XIV 


CONTENTS. 

PAGE. 

Cornu  commissural 178 

Septo-marginal 178 

Comma 178 

Posteromedian  (Goll) 179 

Lesions  in  posterior  columns 179 

Roots  of  spinal  nerves 179-182 

Anterior  roots 180 

Origins— superficial  and  deep 180 

Lesions  of  lower  motor  neurones 180 

Posterior  roots 180-182 

Central  terminations 181 

Superficial  (apparent) 181 

Deep  (real) 181-182 

Lesions  of  posterior  roots 182 

Blood  supply  of  the  cord 182-184 

Chapter  X. 

Tracing  of  Impulses 185-201 

Efferent,  or  motor,  paths,  through 185-190 

Pyramidal  tracts 185-186 

Frontal  cerebro-corticopontal  tract 186-187 

Temporal  cerebro-corticopontal  tract 187 

Intermediate  bundle 187 

Red  nucleus — direct  and  indirect 188 

Short  fiber  paths  (formatio  reticularis) 188-190 

Facial  paralysis,  nuclear  and  nerve  trunk 189 

Abducent  paralysis  and  irritation 189-190 

Afferent  paths,  general  sensation 190-193 

Columns  of  Goll  and  Burdach 190-192 

Direct 190-191 

Indirect 191-192 

Cranial  nerves  and  medial  fillet 191 

Direct  cerebellar  tract 191-192 

Antero-lateral  ascending  cerebellar  tract 192-193 

Short  fiber   paths  (antero-lateral  ground  bundle)....        193 

Lesions  of  sensory  tracts. . 193 

Afferent  paths,  special  sense. 194-197 

Olfactory 194 

XV 


CONTENTS. 

PAGE. 

Optic 194-195 

Auditory .' 195-197 

Cochlear 195 

Vestibular 196 

Gustatory 197 

Lesions  of  special  sense  tracts 197 

Reflex  paths 198-201 

Varieties  of  reflex  arcs 198 

Spinal  reflexes 198-199 

Defecation,  etc 198-199 

Cranial  reflexes 199 

Spinal  and  cranial  reflexes 199-200 

Cranial  and  spinal  reflexes 200-201 

Respiratory '. 200 

Auditory 200 

Pupillary 200-201 

Chapter  XI. 

Embryology  of  Brain  and  Spinal  Cord 202-224 

Neural  crest 202-204 

Cranial  nerve  ganglia 202-203 

Spinal  and  sympathetic  ganglia 203-204 

Neural  tube , 204-224 

Three  histologic  layers 205 

Neurogliar 205 

Mantle 20J 

Ependymal 205 

Flexures 206 

Table  III.     Brain  vesicles  and  derivatives 207-208 

1.     Prosencephalon 208-213 

Hemisphere  vesicles 208-213 

Foramen  of  Monro  and  lateral  ventricles.        208 

Olfactory  lobe 208 

Fissures,  primary  and  permanent 209-210 

Special  thickenings 210-211 

Fusion  of  Hemispheres  with  one  another. .  211-212 

Fusion  with  thalamencephalon 212 

Velum  interpositum 212-213 

XVI 


CONTENTS. 

PAGE. 

2.  Thalamencephalon 213-214 

Optic  vesicle 213 

Thalamus 214 

External  geniculate  body 214 

Posterior  commissure 214 

Pineal  body. 214 

3.  Mesencephalon 214-215 

Tegmentum 215 

Corpora  quadrigemina 215 

Internal  geniculate  body 215 

Aqueduct  of  Sylvius 214 

Substantia  nigra 215 

Crustae 215 

4.  Epencephalon 215-216 

Cerebellum 215-216 

Vermis 216 

Hemispheres , 216 

Penduncles 216 

Pons 216 

Nuclei  of  pons 216 

Nuclei  of  cranial  nerves 216 

5.  Metencephalon 217-219 

Internal  surface 218 

External  surface 218 

Three  histologic  layers 218-219 

Ependymal 218 

Mantle 218-219 

Neurogliar 219 

Spinal  cord 220-224 

Ventral  and  dorsal  zones 220-221 

Histologic  layers ,        221 

Mantle  layer — gray  substance 221-222 

Tracts  of  fibers— when  meduUated 222-223 

Fissures  of  cord 223-224 


XVII 


CHAPTER   I. 


THE   MENINGES   OF  THE  BRAIN.i 

Three  membranes  invest  the  brain  and  spinal  cord.  They 
are,  from  without  inward,  the  Dura  Mater,  the  Arachnoid, 
and  the  Pia  Mater.  Each  membrane  forms  a  protecting 
sheath  for  the  cranial  or  spinal  nerves  piercing  it. 

THE  DURA   MATER.2 

Structure  and  Relations. — It  is  a  very  dense  and  inelastic 
membrane  composed  of  white  fibrous  and  yellow  elastic  tissue. 
It  is  lined  with  flat  endothelial  cells  which  constitute  its 
internal  surface.  The  dura  is  made  up  of  two  layers,  but 
they  are  in  most  places  closely  united.  The  external  layer 
constitutes  the  endosteum  of  the  cranial  bones.  It  is  their 
nutrient  membrane.  Through  the  cranial  foramina  and 
sutures  it  is  continuous  with  the  external  periosteum.  The 
internal  layer  of  the  dura  separates  from  the  outer  layer,  at 
the  foramina,  to  form  sheaths  for  the  nerves  and,  along 
the  sinuses,  to  form  the  internal  boundary  of  those  venous 
spaces  and  to  produce  the  great  incomplete  partitions,  called 
processes,  which  project  centrally  into  the  great  fissures  of 
the  brain. 

Processes. — From  the  inner  surface  of  the  dura  the  great 
processes^  are  given  off.  The  falx  cerebri  and  falx  cerehelU 
hang  vertically  in  the  great  longitudinal  fissure  of  the  cere- 

(1)    Meninges   encephali.  (3)    Processus  durae  matrls. 

<2)  Dura  mater  encephali. 


2  THE    BRAIN   AND   SPINAL    CORD. 

brum  and  the  posterior  notch  of  the  cerebellum ;  and,  into 
the  great  transverse  fissure,  extends  horizontally  the  ten- 
torium cerebelU.  The  falx  cerebri  is  attached  in  front  to 
the  crista  galli  and  behind  to  the  internal  occipital  protuber- 
ance and  superior  surface  of  the  tentorium;  the  falx  cere- 
belli  continues  from  the  inferior  surface  of  the  tentorium, 
along  the  occipital  crest,  to  the  posterior  border  of  the  fora- 
men magnum.  The  attachment  of  the  tentorium  cerebelli 
is  to  the  internal  protuberance  and  the  lateral  arms  of  the 
crucial  ridge  forward  to  the  petrous  bone;  and,  then,  it  is 
along  the  superior  border  of  the  petrous  bone  to  the  clinoid 
processes  of  the  sphenoid.  A  large  median  notch  between 
its  anterior  border  and  the  dorsum  ephipii,  incisura  tentorii, 
transmits  the  mid-brain.  The  diaphragm  sellce  is  a  small 
centrally  perforated  sheet  of  dura  which  covers  the  pituitary 
fossa. 

Sinuses. — Large  venous  passages  lined  with  endothelial 
cells,  and  called  sinuses,  are  situated  between  the  layers  of 
the  dura.  In  the  convex  and  in  the  free  border  of  the  falx 
cerebri  are,  respectively,  the  superior^  and  the  inferior^  lon- 
gitudinal sinus.  The  superior  extends  from  the  foramen 
cascum  back  to  the  torcular  HeropMli,^  at  the  internal  occip- 
ital protuberance.  Joining  the  common  vein^  of  Galen,  at 
the  margin  of  the  tentorium,  the  inferior  longitudinal  sinus 
becomes  the  straight,'^  whose  course  is  through  the  middle  of 
the  tentorium  to  the  torcular.  The  occipital  sinus^  (or 
sinuses)  traverses  the  falx  cerebelli  from  the  foramen  mag- 
num upward  to  the  same  point.  In  the  torcular  Herophili 
the  lateral  sinv^es^  rise.     Grooving  the  horizontal  arms  of 

(4)  Sinus  sag-ittalis  superior,  et  inferior. 

(5)  Confluens  sinuum, 

(6)  Vena   cerebri   magna. 

(7)  Sinus  rectus. 

(8)  Sinus  occipitalis. 

(9)  Sinus   traversus    (singr.). 


THE    MENINGES    OF    THE    BRAIN.  3 

the  crucial  ridge,  each  runs  outward  in  the  tentorium  to 
the  base  of  the  petrous  bone,  where  it  receives  the  superior 
petrosal  sinus;  it  then  turns  downward  through  the  sig- 
moid fossa  and  unites  with  the  inferior  petrosal  sinus  in  the 
jugular  foramen.  Situated  on  either  side  of  the  sella  Tur- 
cica is  a  continuation  of  the  ophthalmic  vein,  the  large 
cavernous  sinus,^^  whose  division  at  the  apex  of  the  petrous 
bone  forms  the  two  petrosal  sinuses.^^  The  circular  sinus^^ 
(around  the  sella)  joins  the  two  cavernous  to  each  other; 
and  the  inferior  petrosal  sinuses  communicate  with  one  an- 
other through  the  transverse  or  basilar  sinus.'^^  The  petrosal 
sinuses,  from  the  bifurcation  of  the  cavernous  sinus,  follow 
outward  the  corresponding  border  of  the  petrous  bone;  the 
superior  petrosal  empties  into  the  lateral  sinus  at  the  base  of 
the  petrous  bone;  and  the  inferior  petrosal,  running  outward 
to  the  jugular  foramen,  unites  with  the  lateral  sinus  in 
forming  the  internal  jugular  vein. 

Along  and  within  the  superior  longitudinal  sinus  are  the 
Pacchionian  bodies.^*  They  are  enlarged  villi  of  the  arach- 
noid, and  seem  to  afford  an  outlet  for  the  sub-arachnoid  fluid 
into  the  superior  longitudinal  sinus. 

The  arteries  which  supply  the  dura  are  the  anterior  and 
posterior  ethmoidal  from  ophthalmic;  from  internal  carotid, 
the  anterior  meningeal ;  the  great  and  small  meningeal  which 
are  branches  of  internal  maxillary;  meningeal  branches  of 
the  ascending  pharyngeal  and  occipital;  and  the  posterior 
meningeal  from  the  vertebral  artery. 

The  middle  meningeal^^  is  largest.    It  is  accompanied  by 

(10)  S.  cavernosus. 

(11)  Sinus  petrosus  superior,   et  inferior, 

(12)  S.   circularis. 

(13)  S.  basilarls. 

(14)  Granulatlones  arachnoldeales. 
(16)  Arteria  menlngea  media. 


4  THE    BRAIN   AND   SPINAL    CORD. 

a  vein  and  surgically  is  important  because  of  its  course  over 
the  motor  area.  Ascending  from  the  foramen  spinosum  it 
divides  near  the  upper  border  of  the  squamosa  into  two  large 
branches,  the  anterior  and  posterior.  The  posterior  runs 
horizontally  backward  just  below  the  squamo-parietal  suture 
and  then  ascends  over  the  posterior  half  of  the  parietal  bone. 
The  anterior  branch  runs  upward  a  half-inch  behind  the 
coronal  suture.  It  may  be  located,  according  to  Quain,  at  one 
inch,  one  inch  and  a  half,  and  two  inches  behind  external 
angular  process  and  above  the  zygoma. 

The  following  nerves  give  branches  to  the  dura: — troch- 
lear, ophthalmic,  Gasserian  ganglion,  the  tenth  and  twelfth 
cranial;  and  the  sympathetic.  The  motor  fibers  supply  the 
meningeal  arteries. 

Six  points  of  difference  in  the  dura  of  the  cord. — Absence 
of  processes,  of  sinuses,  of  Pacchionian  bodies,  and  of  perios- 
teal function.  It  is  covered  on  both  surfaces  by  endothelium 
and  separated  from  the  vertebrae  by  areolar  tissue,  fat  and 
the  meningo-rachidian  veins. 

ARACHNOID   OF  BRAIN. 

In  structure  it  is  a  delicate,  fibrous,  web-like  membrane 
covered  externally  with  endothelium.  Internally  it  is  joined 
to  the  pia  mater  by  innumerable  fibrous  trabeculae,  the  sub- 
arachnoid tissue.  The  trabeculae  and  all  spaces  formed  by 
them  possess  a  single  layer  of  endothelial  cells.  Conical 
elevations  of  fibrous  tissue  with  their  investing  epithelium 
constitute  the  villi  seen  on  the  outer  surface. 

Relations. — The  arachnoid^^  follows  the  inner  surface  of 
the  dura  and  is  prolonged,  as  a  sheath,  upon  the  nerves  which 
pierce  it.    It  does  not  dip  into  the  sulci  of  the  brain.    From 

(16)    Arachnoidea  enciephall. 


THE    MENINGES   OF    THE    BRAIN.  5 

the  pia  it  is  separated  by  the  subarachnoid  spaces.^  "^  The  cm- 
tenor  subarachnoid  space  (cisterna  pontis,  interpeduncularis 
et  chiasmatis),  in  front  of  the  medulla,  pons  and  mid-brain 
and  between  the  temporal  lobes  of  the  cerebrum;  and  the 
posterior  (cisterna  cerebello-medullaris) ,  between  the  me- 
dulla and  cerebellum,  contain  most  of  the  subarachnoid,  fluid. 
The  posterior  communicates  with  the  fourth  ventricle 
through  the  foramen  of  Magendie^^  and  the  foramina  of  Key 
and  Retzius.^^ 

The  vessels  seen  for  a  short  distance  in  the  arachnoid 
belong  to  the  pia  mater.  Its  nerves  are  doubtful.  Perhaps 
branches  of  the  inferior  maxillary,  of  the  facial  and  of  the 
spinal  accessory  supply  it. 

In  the  arachnoid  of  the  cord  fewer  trabeculae  join  it  to  the 
pia;  and  these,  in  great  part,  are  collected  to  form  a  fenes- 
trated septum  in  the  posterior  median  line.  The  medulli- 
epinal  veins  are  covered  by  the  arachnoid,  lying  between  it 
and  the  pia. 

PIA   MATEE   OP   TEffi   BRAIN.20 

Structure. — It  is  a  vascular  membrane  composed  of  a  close 
network  of  veins  and  arteries  held  together  by  fibro-elastic 
areolar  tissue.  The  endothelium  covering  its  outer  surface 
is  contiuuous  with  that  of  the  subarachnoid  trabeculaB  and 
spaces.  Relations. — The  pia  closely  follows  the  brain  sur- 
face. Internally,  it  sends  supporting  trabeculss  into  the 
brain,  which  transmit  blood-vessels;  and  externally  it  forms 
an  investing  sheath  for  the  cranial  nerves.  TVo  important 
processes  are  formed  by  it;  the  velum  interpositum  (which 
forms  the  superior  choroid  tela^i)  is  tucked  into  the  choroid 

(17)  Cavum   subarachnoldeale    (sing.). 

(18)  Apertura  medlana  ventricull  quartl. 

(19)  Apertura  lateralis  ventriculi  quart!   (slng.)> 

(20)  Pia  mater  encephali. 

(21)  Tela  choroidea  ventriculi  tertii. 


O  THE    BRAIN   AND   SPINAL    CORD. 

(anterior  great  transverse)  fissure  between  the  fornix  and 
the  inter-brain.  A  second  process  is  tucked  in  over  the  fourth 
ventricle,  between  the  medulla  and  cerebellum.  It  forms  the 
inferior  choroid  tela,22  which  roofs  over  the  inferior  part 
of  the  fourth  ventricle,  and  is  of  triangular  shape.  The 
inferior  choroid  tela  is  pierced  by  three  foramina  (Magen- 
die,  and  Key  and  Retzius).  They  open  into  the  fourth 
ventricle. 

The  arteries  of  the  pia  are  the  anterior,  middle  and  pos- 
terior cerebral,  the  anterior  and  posterior  choroids,  and  the 
anterior  and  posterior  inferior  cerebellar  and  superior  cere- 
bellar with  many  branches. 

Veins  are  numerous  in  the  pia;  the  veins  of  Galen  and 
of  the  choroid  plexuses  of  the  lateral,  third  and  fourth 
ventricles  and  the  basilar  vein;  cerebral  veins;,  superior, 
medial  and  inferior;  and  superior,  lateral  and  inferior  cere- 
bellar veins.    All  of  them  empty  into  the  sinuses. 

Seven  cranial  nerves — 3rd,  5th,  6th,  and  7th,  9th,  10th 
and  11th — and  the  sympathetic  supply  the  pia  mater  and  its 
blood-vessels. 

The  pia  mater  of  the  spinal  cord  has  two  layers,  the  outer 
of  which  is  the  more  vascular  and  contains  the  spinal  arteries 
and  the  tributaries  of  the  meduUi-spinal  veins.  It  forms 
three  processes,  namely,  the  anterior  septum,  which  occupies 
the  anterior  median  fissure,  and  the  ligamentum  denticu- 
latum  of  each  side. 

TABLE    1. 

GRAND  DIVISIONS   OF  BRAIN. 

The  brain  may  be  conveniently  studied  in  four  grand 
divisions : 

(22)    Tela  choroidea  ventriculi  quarti- 


THE    MENINGES    OF   THE   BRAIN  7 

I.  Cerebrum,23  composed  of — 

1.  Heinisplieres,2*  which  include: 

Their  cortex  and  medulla. 
Corpora  striata,  and 
Olfactory  lobes. 

With  connecting  links  of  the  hemispheres : 

Corpus  callosum. 

Fornix, 

Commissura  hippocampi  and 

Anterior  commissure;  and 

2.  Inter-brain,25    or    Thalamencephalon,    which    in- 

cludes : 
Lamina  cinerea, 

Tuber  cinereum  and  infundibulum, 
Corpora  albicantia. 
Optic  thalami. 

Middle  commissure,  and  posterior  (in  part). 
Pineal  body, 

External  geniculate  bodies. 
Optic  tracts  and  commissure. 
II.  Mid-brain,  Cms  Cerebri,  or  Pedunculus  Cerebri^^ 
Crustae,  (the  bases  or  pedes  pedunculi) 
Substantia  nigra 
Tegmentum 
Corpora  quadrigemina 
Internal  geniculate  bodies. 

III.  Hind-brain27-_ 

Pons 
Cerebellum. 

IV.  After-brain^s — 

Medulla. 

(23)  Prosencephalon.  (26)    Mesencephalon. 

(24)  Telencephalon.  (27)    Metencephalon. 

(25)  Diencephalon.  (28)     Myelencephalon. 


CHAPTER  II. 


THE  CEREBRUM. 

The  cerebrum  is  that  part  of  the  brain  which  especially 
characterizes  man.  In  man  only  does  it  reach  such  predom- 
inant development.  Though  a  mere  outgrowth  of  the  an- 
terior brain-vesicle  in  the  beginning,  it  completely  overshad- 
ows all  other  parts  of  the  brain  by  the  seventh  month  of  em- 
bryonic life,  extending  farther  forward,  backward  and  lat- 
eral ward  than  any  other  part.  Reference  to  the  table  given 
above  shows  that  the  cerebrum  is  made  up  of  the  hemispheres 
and  the  inter-hrain.  It  constitutes  an  ovoid  mass,  flattened 
inferiorly,  which  fills  the  vault  of  the  cranium  and  rests,  be- 
low, upon  the  floor  of  the  cranial  cavity  in  the  anterior  and 
middle  fossae  and  upon  the  tentorium  cerebelli  over  the  pos- 
terior fossa.  Viewed  from  above,  it  is  sufficiently  round 
to  suggest  a  sphere ;  and,  being  divided  in  the  median  line  by 
the  great  longitudinal  fissure,  the  lateral  halves  are  called 
hemispheres.  In  the  floor  of  the  great  longitudinal  fissure 
the  corpus  callosum  can  be  seen  joining  the  hemispheres  to- 
gether; and  beneath  it,  concealed  from  view,  are  the  fornix, 
anterior  commissure,  and  commisura  hippocampi.  Those  are 
the  connecting  links,  proper,  of  the  hemispheres.  Inferior 
to  them,  is  found  the  inter-brain.  The  latter  forms  an  addi- 
tional union  of  the  hemispheres,  as  may  be  seen  by  viewing 
the  base  of  the  brain.  In  order  to  fix  important  landmarks 
and  to  learn  the  location  and  relations  of  the  gross  structures 


THE    CEREBRUM.  9 

of  the  cerebrum,  it  is  necessary  to  study  in  detail  the  topogra- 
phy of  the  exterior  and  interior  surface.  It  is  that  with  which 
the  present  chapter  deals.  For  the  minute  anatomy  of  the 
cerebral  structures,  see  Chapter  IV. 

Section  1.    The  Exterior  Surface. 

The  exterior  surface  of  the  cerebrum^  is  composed  of  a 
thin  sheet  of  gray  matter  varying  in  thickness  from  one- 
sixth  to  one-quarter  of  an  inch.  That  gray  matter  forms  a 
bark-like  covering  for  the  underlying  white  substance  and 
is,  therefore,  called  the  Cortex.  It  is  thrown  into  irregular 
elongated  folds  named  Convolutions,  or  Gyri,  by  deep  linear 
depressions,  which  greatly  increase  the  relative  amount  of 
cortical  substance.  The  linear  depressions  are  called  Fis- 
sures, or  Sulci;  and,  in  consequence  of  them,  the  gray  sub- 
stance is  increased  in  bulk  to  58^  per  cent  of  the  entire  cere- 
brum (De  Eegibus). 

The  exterior  surface  is  conveniently  studied  in  three  re- 
gions, namely,  the  Convex  Surface,  the  Medial  and  Tento- 
rial Surface,  and  the  Basal  Surface. 

FISSURES    OF   the    CONVEX   SURFACE.^ 

Two  fissures  are  very  extensive.  The  great  longitudinal 
fissure^  separates  the  hemispheres  of  the  cerebrum.  It  con- 
tains the  falx  cerebri.  The  cerebrum  is  separated  from  the 
cerebellum  by  the  great  transverse  fissure.*  This  fissure 
continues  forward  above  the  mid-brain,  and  terminates  in  the 
cerebrum  between  the  inter-brain  and  the  hemispheres  as 
choroid  fissure.  The  tentorium  occupies  its  posterior  part. 
The  fissura  choroidea  contains  the  velum  interpositum.  Three 

(1)  Prosencephalon. 

(2)  Facies   convexa. 

(3)  Fissura  longitudinalis  cerebri. 

(4)  Fissura  transversa  cerebri. 


10  THE    BRAIN    AND   SPINAL   CORD. 

interlobular  fissures^  are  found  on  the  convex  surface  of  each 
hemisphere  : 

(1)  The  Fissure  of  Sylvius^  begins  in  the  vallecula  at  the 
base  of  the  brain.  It  runs  outward  between  the  frontal  and 
the  temporal  lobe^  along  the  lesser  wing  of  the  sphenoid  bone ; 
and^  turning  upward,  on  the  convex  surface  it  divides  into 
an  anterior,  a  vertical  and  a  horizontal  ramus.  Into  the 
frontal  lobe  project  the  small  anterior  and  vertical  rami. 
They  are  separated  by  the  foot  (posterior  end)  of  the  inferior 
frontal  gyrus,  called  the  frontal  operculum  (operculum,  a 
cover).  Below  the  anterior  ramus  is  a  knuckle  of  the  same 
frontal  convolution  which  forms  the  orbital  operculum;  and, 
between  the  vertical  and  horizontal  rami,  is  located  the 
fronto-parietal  operculum,  constituting  the  connecting  gyrus 
between  the  precentral  and  postcentral  convolutions.  The 
opercula  cover  the  island  of  Eeil.  The  horizontal  limb  of 
the  Sylvian  fissure  separates  the  temporal  lobe  from  the 
parietal.  Near  the  crotch  and  within  the  fissure  of  Sylvius 
is  situated  the  island  of  Eeil.  A  line  drawn  from  the  Sylvian 
point,  one  and  one-quarter  inches  behind  the  external  angu- 
lar process  of  the  frontal  and  one  and  a  half  inches  above  the 
zygoma,  backward  to  a  point  three-quarters  of  an  inch  below 
the  parietal  eminence,  lies  directly  over  the  horizontal  ramus 
of  this  fissure. 

(2)  Fissure  of  Rolando. — Beginning  just  above  the  hori- 
zontal limb  of  the  fissure  of  Sylvius,  is  the  fissure  of  Eolando, 
or  Central  fissure,^  which  extends  upward  and  backward 
almost  to  the  great  longitudinal  fissure.  Its  upper  extrem- 
ity is  about  half  an  inch  behind  the  middle  of  a  line  drawn 
from  the  nasal  eminence  to  the  external  occipital  protuber- 

(5)  Fissurse  interlobulares.  (7)     Sulcus   centralis. 

(6)  Fissura  lateralis  cerebri. 


THE    CEREBRUM.  II 

ance  (the  sagittal  meridian).  With  this  line  the  fissure  of 
Rolando  forms  an  anterior  angle  of  67  to  73  degrees.  The 
fissure  of  Rolando  forms  the  boundary  between  the  frontal 
and  the  parietal  lobe.  It  is  developed  in  two  parts,  superior 
and  inferior,  which  join  at  an  angle  open  backward,  the  genu, 
and  both  parts  may  present  an  anterior  concavity. 

(3)  Parieto-occipital  Fissure.^ — If  the  line  locating  the 
horizontal  limb  of  the  fissure  of  Sylvius  be  extended  back  to 
the  sagittal  meridian  its  posterior  end  marks  the  location  of 
the  parieto-occipital  fissure  (external  part).  The  greater 
part  of  this  fissure  is  on  the  internal  or  medial  surface  of 
the  hemisphere.  To  the  extent  of  half  an  inch  the  external 
parieto-occipital  fissure  separates  the  parietal  and  occipital 
lobes  from  each  other. 

LOBES    AND   CONVOLUTIONS   OP   THE   CONVEX   SURFACE. 

(I)  The  Frontal  Lobe^  comprises  the  anterior  polar  region 
of  the  hemisphere  back  to  the  Rolandic  and  the  Sylvian  fis- 
sure. It  is  subdivided  by  three  sulci:  The  precentral 
sulcus^^  (superior  and  inferior  parts),  which  is  parallel  with 
the  fissure  of  Rolando  (central),  and  the  superior  and  infe- 
rior frontal  sulci.^i  ^he  two  latter  extend  downward  and 
forward  from  superior  and  inferior  precentral  sulci,  respec- 
tively, and  separate  from  each  other  the  superior,  middle  and 
inferior  frontal  convolutions.^^  The  ascending  frontal  con- 
volution^^ (precentral)  lies  between  the  precentral  sulcus  and 
the  fissure  of  Rolando.  It  is  joined  to  the  ascending  parietal 
convolution^^     (postcentral)    by    the    paracentral    lobule,^* 

(8)  Sulcus  occipito-parietalla. 

(9)  Lobus  frontalis. 

(10)  Sulcus  prsecentralia. 

(II)  S.  frontalis  superior.  Inferior. 

^  (12)    Gyrus  frontalis  superior,  medius.  Inferior. 

(13)  G.  centralis  anterior,  posterior. 

(14)  Lobulus   paracentralis. 


12  THE   BRAIN   AND   SPINAL    CORD. 

above  the  central  fissure,  and  by  the  fronto-parietal  opercu- 
lum, below  it.  The  fronto-parietal  operculum  and  posterior 
part  of  the  inferior  frontal  gyrus  constitute  the  region  of 
speech.  In  the  foot  (posterior  end)  of  the  middle  frontal 
gyrus  is  the  writing  center  (Gordinier). 

(2)  The  Parietal  Lobe^^  is  situated  behind  the  fissure  of 
Eolando  and  above  the  horizontal  limb  of  the  Sylvian  fissure. 
From  the  posterior  end  of  the  latter  to  the  external  parieto- 
occipital fissure,  the  lobe  is  separated  from  the  temporal, 
below,  and  the  occipital,  behind,  by  an  imaginary  line.  The 
sulci  of  this  lobe  are  the  intraparietal,^  ^  with  an  anterior 
and  a  posterior  ramus  (joined  by  the  genu)  which  are  par- 
allel with  the  central,  and  the  great  longitudinal  fissures, 
respectively;  and  the  postcentral  sulcus,^^  which  ascends 
from  the  genu  of  the  intraparietal  almost  to  the  great  longi- 
tudinal fissure.  The  anterior  limb  of  the  intraparietal  fis^ 
sure  and  the  postcentral  sulcus  separate  the  ascending  pa- 
rietal convolution^^  from  the  superior  parietal  and  inferior 
parietal.^  ^  The  posterior  limb  of  the  intraparietal  fissure 
separates  the  superior  and  inferior  parietal  convolutions  from 
each  other.  Indefinite  sulci  subdivide  the  inferior  parietal 
into  supra-marginalj^^  angular J^^  and  postparietal  gyri,  which 
wind  over  the  upturned  ends  of  the  Sylvian  and  first  and 
second  temporal  sulci,  respectively.  The  best  known  motor 
areas  of  the  cortex  are  contained  in  the  ascending  frontal, 
ascending  parietal  and  superior  parietal  gyri ;  in  the  foot  of 
the  inferior  and  middle  frontal  convolutions;  in  the  quad- 
rate and  paracentral  lobules,  and  in  the  marginal  gyrus. 

(15)  Lobus  parietalis. 

(16)  Sulcus  interparietalis. 

(17)  S.   postcentralis. 

(18)  Gyrus  centralis  posterior. 

(19)  Lobulus  parietalis  superior,  inferior. 

(20)  Gyrus  supramarginalis. 

(21)  Gyrus  angularis. 


THE    CEREBRUM.  I 3 

The  area  of  general  sensation,  somcesthetic  area/^^  nearly 
coincides  with  the  great  motor  areas;  it  is  a  little  more  ex- 
tensive as  it  includes  much  of  the  limbic  lobe. 

(3)  Occipital  Lobe.^s — It  forms  the  posterior  pole  of  the 
hemisphere.  With  the  parietal  and  temporal  lobes  it  is  di- 
rectly continuous,  being  marked  off  from  them  by  an  imag- 
inary line  drawn  from  the  preoccipital  notch  to  the  external 
parieto-occipital  fissure.  The  parieto-occipital  fissure  bounds 
it  to  the  extent  of  half  an  inch;  rarely,  the  external  perpen- 
dicular fissure  bounds  it  in  front.  Its  sulci^*  and  convolu- 
tions vary  much ;  usually  the  following  are  found :  The  su- 
perior occipital  sulcus,  vertical,  or  longitudinal,  in  direction, 
and  the  middle  and  inferior,^*  which  are  horizontal,  divide 
the  lobe  into  superior,  middle  and  inferior  convolutions.^^ 
The  superior  occipital  sulcus  is  often  continuous  with  the  in- 
traparietal  fissure.  The  inferior  occipital  sulcus  follows  the 
lower  border  of  the  convex  surface.  The  superior  and  infe- 
rior convolutions  form  the  corresponding  borders  of  the  lobe 
and  trend  toward  the  occipital  pole.  The  middle  occipital 
gyrus  is  in  the  angle  between  them  and  may  reach  the  medial 
border.  The  visual  memory  center  is  located  in  the  convex 
surface  of  the  occipital  lobe  and  in  the  angular  gyrus. 

(4)  The  Temporal  Lobe^e  is  that  part  of  the  cerebral  hemi- 
sphere behind  the  main  stem  and  below  the  horizontal  limb  of 
the  fissure  of  Sylvius.  It  rests  in  the  middle  fossa  of  the 
skull;  and  is  probably  the  seat  of  the  centers  of  taste,  smell 
and  hearing.  The  first  temporal  sulcus^'^  (or  parallel  sulcus) 
and  the  second  temporal  sulcus^^  divide  the  lobe  into  three 

(22)  Soma—hody—Aesthesis—iterce^tiojh,  or  feeling. 

(23)  Lobus  occipitalis. 

(24)  Sulci  occipitales  laterales.    S.  oc.  transversus. 
(,2S)  Gyri  occipitales  laterales. 

(26)  Lobus  temporalis. 

(27)  Sulcus  temporalis  superior,   medius. 


14  THE    BRAIN   AND   SPINAL    CORD. 

horizontal  convolutions,  named,  from  the  Sylvian  fissure 
downward,  the  first,  second  and  third  temporal  convolutions.^^ 
In  the  third  and  fourth  fifths  of  the  first  temporal  convolu- 
tion, and  in  the  transverse  temporal  gyri,  concealed  in  the 
fissure  of  Sylvius,  is  the  receptive  center  of  hearing  (Barker). 

Annectant  convolutions  are  small  links  joining  the  greater 
gyri.  The  first  annectant  joins  the  superior  parietal  and  su- 
perior occipital  convolutions.  To  the  middle  occipital  gyrus, 
the  angular  or  postparietal  is  linked  by  the  second  annectant 
and  the  middle  temporal  by  the  third.  The  fourth  annectant 
unites  the  inferior  temporal  and  inferior  occipital  convolu- 
tions.    There  are  other  less  constant  annectants. 

(5)  The  Island  of  Reil29  is  also  called  the  central  lobe. 
Situated  within  the  fissure  of  Sylvius,  it  is  bounded  at  the 
base  of  the  brain  by  the  sulcus  limitans  insulae  (anterior, 
external  and  posterior)  .^o  The  sulcus  centralis  insulae  di- 
vides it  into  anterior  and  posterior  lohule,  each  of  which  is 
composed  of  from  two  to  four  convolutions.^^  The  fronto- 
parietal operculum  and  inferior  frontal  convolution,  together 
with  the  temporal  lobe,  cover  the  insular  convolutions,  hence 
the  name,  gyri  operti,  also  applied  to  thein. 

FISSURES  OF  THE  MEDIAL  AND  TENTORIAL  SURFACE. 

The  middle  third  of  this  surface^^  fg  made  by  sagittal  sec- 
tion through  the  connecting  links  of  the  hemispheres  and 
the  inter-brain.    The  free  surface  presents  six  fissures. 

(1)  Calloso-marginal  Fissure. — Beginning  under  this  mid- 
dle cut  surface  and  extending  forward,  upward  and  backwanl 
until  it  half  encircles  the  corpus  callosum;  and  then  tum- 

(28)  Gyrus  temporalis  superior,  medius,  inferior. 

(29)  Insula. 

(30)  Sulcus  circularis   (Reili). 

(31)  Gyri  insulae— G.  breves,  Gyrus  longus. 

(32)  Facies  medialis. 


THE    CEREBRUM.  1 5 

ing  upward  to  the  convex  border  and  ending  just  behind  the 
fissure  of  Rolando,  is  the  calloso-marginal  fissure.^^  It  sep- 
arates the  gyrus  fornicatus  and  the  marginal  convolution 
from  one  another  by  its  anterior  part;  and,  by  its  upturned 
posterior  end,  separates  the  paracentral  lobule  from  the  quad- 
rate lobe. 

(2)  The  Parieto-occipital  Fissure  (internal  part)^*  ex- 
tends upward  and  backward  from  just  beneath  the  thick  pos- 
terior margin  of  the  corpus  callosum,  the  splenium,  to  the 
border  of  the  medial  surface,  where  it  is  continuous  with  the 
external  parieto-occipital  fissure.  It  is  situated  between  the 
quadrate  and  the  cuneate  lobe. 

(3)  Calcarine. — From  near  the  middle  of  the  parieto- 
occipital, the  calcarine  fissure^^  extends  in  a  curve  downward 
and  backward  between  the  cuneate  lobe  and  the  fifth  temporal 
(lingual)  convolution  and  ends  bifid.  The  anterior  part  of 
the  parieto-occipital  fissure,  in  its  formation,  may  be  com- 
mon either  to  that  fissure  or  to  the  calcarine, 

(4)  Hippoeampal  Fissure. — A  crescentic  fissure,  convex 
downward,  winds  from  the  splenium  of  the  corpus  callosum 
forward  beneath  the  optic  thalamus  nearly  to  the  end  of  the 
temporal  lobe,  where  it  is  closed  by  the  uncus.  It  is  the  den- 
tate or  hippoeampal  fissure.^^  On  the  surface  of  the  temporal 
lobe  this  fissure  appears  to  be  identical  with  the  temporal 
extension  of  the  great  transverse  fissure,  the  choroid  fissure; 
but,  deeply,  it  lies  posterior  to  it  and  is  separated  from  the 
choroid  fissure^"^  by  the  fascia  dentata. 

(5)  Choroid  Fissure. — It  is  of  horseshoe  shape  and  extends 
from  the  foramen  of  Monro  backward, — ^and  downward, — and 
forward  to  near  the  pole  of  the  temporal  lobe.     On  its  con- 

(88)    Sulcus  cinguli.  (36)    F.  hippocampi. 

(34)  S.   parieto-occipitalls.  (37)    Fissura  choroldea. 

(35)  Fissura  calcarina. 


l6  THE    BRAIN   AND   SPINAL    CORD. 

vexity  it  is  bounded  by  the  fornix.  The  fissure  is  a  com- 
plete one,  involving  the  whole  hemisphere  wall.  A  single 
lajer  of  epithelium  separates  it  from  the  lateral  ventricle. 
The  pia  mater,  dipping  into  it,  forms  the  choroid  plexus  of 
that  ventricle.  The  fissure  is  again  peculiar  in  the  fact  that 
between  the  roof  of  the  third  ventricle  and  the  fornix  it  is 
directly  continuous  with  the  same  fissure  on  the  opposite  side. 
In  this  antero-superior  part,  which  is  in  direct  continuity 
with  the  great  transverse  fissure,  is  the  velum  interpositum. 

(6)  The  Collateral  Fissure^s  is  situated  below  the  dentate, 
parieto-occipital  and  calcarine  fissures,  and  is  developed  in 
three  parts.  The  collateral  fissure  bounds,  inferiorly,  the  hip- 
pocampal  and  the  fifth  temporal  convolution;  and  separates 
them  from  the  fourth  temporal  (fusiform)  gyrus. 

LOBES    AND    CONVOLUTIONS    OF   MEDIAL   AND   TENTORIAL   SUR- 
FACE. 

They  form  two  concentric  rings,  interrupted  antero-infe- 
riorly  at  the  vallecula  Sylvii,  which  encircle  the  corpus  cal- 
losum  and  optic  thalamus.  The  two  rings  are  separated 
from  one  another  by  a  broken  fissure,  the  limbic  -fissure,  made 
up  of  the  calloso-marginal  (except  its  posterior  end),  the 
post-limbic  sulcus,  and  the  anterior  part  of  the  parieto- 
occipital and  collateral  fissures. 

Central  Ring. — The  gyrus  fornicatus^^  and  hippocampal 
convolution'^^  joined  by  the  isthmus,*^  at  the  posterior  border 
of  the  corpus  callosum,  form  the  central  ring.  The  former 
begins  under  the  corpus  callosum  in  the  frontal  lobe  anterior 
to  the  fissure  of  Sylvius;  and  the  latter  terminates  as  uncus 
just  behind  that  fissure  in  the  temporal  lobe.  The  central 
ring  forms  the  chief  part  of  the  limbic  lobe. 

(38)  Fissura  collateralls.  (40)    Gyrus   hippocampi. 

(39)  Gyrus  cinguli.  (41)    Isthmus  gyri  fornicati. 


THE    CEREBRUM.  I 7 

The  Peripheral  Ringf,  from  before  backward,  is  composed 
of  the  marginal  convolution ^'^^  ending  in  the  paracentral 
lohule^^;  the  quadrate  lohej^^  bounded  anterio-inferiorly  by 
the  postlimbic  sulcus;  the  cuneate  lohe^^j  the  fifth  tempo- 
ral convolution  (infracalcarine,  or  lingual)  ^^;  and  the  fourth 
temporal,  or  fusiform,  convolution^'^  A  slight  sulcus  (third 
temporal)  separates  the  last  from  the  third  temporal  gyrus 
on  the  convex  surface.  The  quadrate  and  paracentral  lob- 
ules and  the  posterior  third  or  half  of  the  marginal  gyrus 
contain  motor  centers,  for  the  opposite  side  of  the  body,  the 
head,  arm,  trunk  and  leg  centers  being  located  in  this  order 
from  before  backward. 

The  uncinate  convolution  is  the  combined  hippocampal 
and  fifth  temporal  gyri. 

Limbic  Lobe. — It  is  composed  of  the  following  parts,  viz. : 
(1)  The  gyrus  fomicatus  and  hippocampal  convolution;  (2) 
the  nerves  of  Lancisi  and  peduncle  of  the  corpus  callosum; 
and  (3)  the  pillars  and  half  the  body  of  the  fornix,  one-half 
of  the  septum  lucidum,  and  the  fascia  dentata.  It  is  encir- 
cled by  the  limbic  fissure.  The  limbic  lobe  probably  con- 
tains the  centers  of  smell  and  taste,  which  are  localized  in  the 
hippocampal  gyrus  and  uncus.  Together  with  the  olfactory 
lobe  it  constitutes  the  Rhinencephalon. 

BASAL  OR  INFERIOR  SURFACE. 

The  basal  surface  of  the  cerebrum^^  comprises  the  inferior 
surface  of  the  hemispheres  and  of  the  inter-brain.  It  ex- 
tends from  the  anterior  poles  of  the  hemispheres  back  to  the 
fissure  of  Sylvius,  laterally;    and,  in  the  median  line,  to  the 

(42)  Gyrus  frontalis  superior.  (46)  Gyrus  lingualis. 

(43)  Lobulus  paracentralis.       ■  (47)  Gyrus  fusiformis. 

(44)  Prsecuneus.  ,  (48)  Facies  basalis  cerebri. 

(45)  Cuneus.  j) 


I8  THE   BRAIN   AND   SPINAL    CORD. 

posterior  perforated  lamina  and  crustse  of  the  mid-brain.  The 
great  longitudinal  fissure  splits  it  into  lateral  halves  in  front, 
separating  the  frontal  lobes  of  the  cerebrum  from  each  other. 
The  fissure  extends  back  to  the  upturned  part  (lamina  ter- 
minalis)  of  the  lamina  cinerea  and  to  the  corpus  callosum. 
The  length  of  the  fissure  is  considerably  less  than  one-third 
of  the  cerebral  axis. 

The  medial  structures  of  this  surface,  named  from  before 
backward,  are  as  follows: 

Lamina  cinerea. 

Optic  chiasm,  or  optic  commissure, 

Tuber  cinereum.  and  infundibulum. 

Pituitary  body. 

Corpora  albicantia. 
These  are  often  called  interpeduncular  structures.  Con- 
stituting the  hase  of  the  inter-hrain,  they  form  a  continuous 
sheet  beneath  the  third  ventricle  and  optic  thalami,  which 
joins,  antero-laterally,  the  anterior  perforated  lamina  and  the 
cortex  of  the  internal  orbital  convolution. 

The  Lamina  Cinerea  is  the  most  anterior  of  the  medial 
structures.  It  is  a  thin  lamina  of  ash-colored  (cinereum) 
gray  matter.  Arching  from  behind  forward  over  the  supe- 
rior surface  of  the  optic  commissure  to  which  it  is  attached, 
it  then  turns  upward  and  backward,  the  reflected  part  con- 
stituting the  lamina  terminalis,  and  meets  the  rostrum  of 
the  corpus  callosum.  In  the  angle  of  turning  is  the  optic 
recess.  The  lamina  terminalis,  which  is  seen  in  the  floor  of 
the  great  longitudinal  fissure,  forms  part  of  the  anterior 
boundary  of  the  third  ventricle. 

Tuber  Cinereum. — At  the  posterior  border  of  the  optic 
commissure,  the  lamina  is  continuous  with  the  tuber  cine- 
reum.   Here  the  gray  matter  is  thickened  and  centrally  prom- 


THE    CEREBRUM,  I9 

inent.  The  bulbous  infundihulum  projects  downward  from 
it  to  rest  in  the  sella  Turcica,  where  it  forms  the  posterior 
lobe  of  the  pituitary  body.  The  upper  half  of  the  infundih- 
ulum is  hollow  (funnel-like).  Its  cavity  forms  the  lowest 
part  of  the  third  ventricle.  In  man  the  bulb  of  the  infundib- 
ulum  is  solid  at  maturity,  though  hollow  in  the  embryo.  It 
is  composed  largely  of  fibrous  tissue,  notwithstanding  the  fact 
that  it  is  developed  from  the  floor  of  the  Thalmencephalon. 
From  the  base  (superior  end)  of  the  infundihulum,  the  tuber, 
cinereum  extends  in  continuity  with  the  anterior  perforated 
lamina  and  hypothalamic  gray  matter  on  each  side  of  it;  and, 
behind,  the  corpora  albicantia  mark  the  boundary  between  it 
and  the  posterior  perforated  lamina  of  the  mid-brain. 

The  lamina  cinerea  and  tuber  cinereum  form  the  inferior, 
or  great,  gray  commissure  of  the  inter-brain. 

The  Pituitary  Body  (hypophysis)  is  composed  of  two  lobes 
bound  together  by  connective  tissue.  A  sheet  of  dura  mater 
(diaphragma  sellae)  holds  them  in  the  pituitary  fossa.  The 
anterior  lohe,  the  larger,  is  derived  from  the  epithelium  of 
the  mouth  cavity;  and,  in  structure,  resembles'  the  thyroid 
gland.  Its  closed  vesicles,  lined  with  columnar  epithelium 
(in  part  ciliated),  contain  a  viscid  jelly-like  material  (pitu- 
ita),  which  suggested  the  name  for  the  body.  The  anterior 
lobe  is  hollowed  out  on  its  posterior  surface  (kidney-shape) 
and  receives  the  posterior  lobe,  the  infundihulum,  into  the 
concavity.  The  pituitary  body  appears  to  have  an  inhibitive 
action  on  growth  and  is  found  diseased  in  acromegalia. 

Corpora  Albicantia. — Two  white  bodies,  as  large  as  a  small 
pea,  the  corpora  albicantia,^^  are  situated  one  on  either  side 
of  the  median  line,  between  the  tuber  cinereum  and  the  pig- 
mented gray  matter  of  the  posterior  perforated  lamina.  Each 

(49)    Corpora  mamillaria. 


20  THE    BRAIN   AND    SPINAL    CORD. 

is  formed  by  a  loop  in  the  anterior  pillar  of  the  fornix  and 
is,  therefore,  composed  of  white  fibers  on  the  surface.  There 
is  gray  matter  in  the  interior,  which  may  contain  the  ends 
of  the  fornix  fibers  and  be  the  seat  of  origin  of  the  ascending 
bundle,  the  bundle  of  Vicq  d'Azyr.^<*  The  latter  terminates 
in  the  optic  thalamus.      (Note  14,  page  226.) 

Immediately  behind  the  corpora  albicantia  is  the  posterior 
perforated  lamina.  This  is  the  exposed  part  of  the  substan- 
tia nigra  of  the  mid-brain,  perforated  for  the  passage  of  the 
postero-median  ganglionic  arteries  to  the  optic  thalami  and 
walls  of  the  third  ventricle.  The  pons  and  crustse  bound  it 
behind.  Issuing  from  the  inner  side  of  the  crusta^^  is  the 
large  motor  oculi,  or  third  cranial,  nerve^^.  qj^^  coursing 
over  its  surface  from  behind  forward,  is  the  smaller  troch- 
lear or  fourth  nerve.^^  The  crustae  will  be  described  with  the 
mid-brain  to  which  they  belong. 

The  Optic  Chiasm  (chiasma  opticum)  remains  to  be  de- 
scribed. It  is  situated  medially  beneath  the  lamina  cinerea, 
in  the  optic  groove  of  the  sphenoid  bone.  The  fibers  of  the 
optic  nerves  and  tracts  compose  it.  There  are  three  sets  of 
these  fibers,  namely,  the  intercerehral,  direct  and  decussat- 
ing. A  fourth  group  of  fibers,  called  interretinal  and  said 
to  be  commissural  for  the  retinae,  has  been  hitherto  described, 
but  their  existence  is  very  doubtful.  The  intercerehral  fibers 
are  not  found  in  the  optic  nerves,  but  form  a  commissure 
(Gudden's)  for  the  internal  geniculate  bodies.  The  direct 
and  decussating  fibers  run  through  tract  and  nerve  and  join 
the  brain  with  the  retina  of  the  same  and  of  the  opposite 
side,  respectively.     In  most  vertebrates  below  mammals  and 

(50)  Fasciculus   thalamomamillaris. 

(51)  Basis  pedunculi   cerebri   (sing.). 

(52)  Nervus  oculomotorius. 

(53)  N.    trochlearis. 


THE    CEREBRUM.  21 

in  the  mouse  and  guinea  pig,  the  optic  fibers  all  decussate  in 
the  chiasm.  Normally  in  man  and  the  higher  mammals, 
the  lateral  half  of  each  retina  receives  direct  fibers  and  the 
medial  half  crossed  fibers.  The  optic  nerves^*  extend  from 
the  front  of  the  commissure  into  the  orbits  through  the  optic 
foramina  and  terminate  in  the  ganglionar  cells  of  the  retinae. 
The  optic  tracts^^  connect  the  commissure  with  the  brain. 
Each  tract  winds  outward  and  backward  around  the  cerebral 
peduncle,  and  divides  into  an  internal  and  an  external  root.^^ 
The  roots  wind  around  the  optic  thalamus  and  disappear 
(superficial  origin)  at  the  corresponding  geniculate  body. 
The  fibers  of  the  external  root  may  be  traced  to  the  external 
geniculate  body  (80  per  cent.  Von  Monokow),  to  the  optic 
thalamus  (nearly  all  the  20  per  cent,  remjaining) ,  and  the 
rest  to  the  anterior  quadrigeminal  body.  The  optic  radiations 
of  the  internal  capsule  connect  these  centers  with  the  medial 
occipital  cortex.  The  internal  root  rises  from  the  internal 
geniculate  body  and  optic  thalamus.  The  nuclei  of  the  optic 
fibers  are  probably  connected  with  the  cerebellum  by  the 
fillet. 

Notice  now  the  hose  of  the  hemispheres,  comprising  the  or- 
bital and  olfactory  lobes. 

Orbital  Lobe. — The  inferior  surface  of  the  frontal  lobe, 
resting  on  the  orbital  plate  of  the  frontal  bone,  is  called  the 
orbital  lobe.^''  It  is  separated  from  its  fellow  by  the  great 
longitudinal  fissure,  and  is  bounded  behind  by  the 
vallecula  Sylvii  and  fissure  of  Sylvius,  overlapped  by  the  tem- 
poral lobe.  More  accurately,  the  posterior  boundary  is  the 
anterior  perforated  space  and  the  anterior  fissure  of  Eeil. 
The  orbital  lobe  is  concave  transversely  aod  is  divided  by  a 

(54)  Nervi  optlci.  (56)    Radix  medialls,  lateralis. 

(55)  Tractus  optlci.  (57)    Lobus  orbitalis. 


22  THE    BRAIN   AND   SPINAL    CORD. 

Triradiate,  or  an  H-shaped  fissure,^^  directed  fore  and  aft, 
into  internal,  anterior  and  posterior  orbital  convolutions.^^ 
The  internal  orbital  convolution  lies  beside  the  great  longi- 
tudinal fissure,  and  is  continuous  with  the  marginal  convolu- 
tion on  the  medial  surface.  Its  anterior  end  joins  the  supe- 
rior frontal  convolution;  its  posterior,  the  trigone  and  area 
of  Broca.  The  internal  orbital  convolution  is  subdivided  by 
the  sulcus  olfactorius,  which  contains  the  olfactory  tract; 
and  that  part  of  the  convolution  medial  to  the  olfactory  fis- 
sure is  called  the  gyrus  rectus.  The  anterior  and  posterior 
orbital  convolutions  may  be  traced  to  the  convex  cerebral 
surface  in  continuity  with  the  middle  and  inferior  frontal 

If  the  anterior  part  of  the  temporal  lobe  be  removed,  the 
under  surface  of  the  island  of  Eeil  is  brought  into  view. 
The  sulcus  limitans  insulse^^  bounds  it  on  three  sides  (ante- 
rior, external  and  posterior),  and  separates  it  from  the  pos- 
terior orbital  gyrus,  in  front;  the  frontal  and  fronto-parietal 
opercula,  externally;  and  from  the  temporal  lobe,  behind. 
(See  lobes  of  convex  surface.) 

Olfactory  Lobe. — This  term  includes  the  remainder  of  the 
structures  forming  the  inferior  surface  of  the  cerebrum.  The 
reason  for  calling  them  the  olfactory  lobe^^  is  found  in  the 
lower  animals;  and  in  the  human  embryo,  where  it  exists  as 
a  prominent  hollow  process  of  the  cerebral  hemisphere.  A 
constriction  (fissura  prima)  divides  this  diverticulum  into  the 
anterior  and  posterior  olfactory  lohule.  In  the  human  adult 
the  anterior  olfactory  lobule  is  represented  by  the  bulb,  the 
tract,  the  trigone  and  the  area  of  Broca.  The  anterior  per- 
forated lamina  (or  space)  represents  the  posterior  lobule. 

The  Olfactory  Bulb^^  is  an  ovoid  mass  of  brain  matter 

(58)    Fissures  orbitales.  (61)    Lobus   olfactorius. 

(69)    Gyri  orbitales.  (62)    Bulbus  olfactorius. 

(60)    Sulcus   circularis    (Reili). 


THE    CEREBRUM.  23 

about  a  half-inch  long  and  one-sixth  of  an  inch  in  diameter. 
It  rests  between  the  orbital  lobe  and  the  cribriform  plate  of 
the  ethmoid  bone.  Below  and  on  each  side,  it  is  composed  of 
cortical  gray  matter  (four  layers)  from  which  rise  the 
twenty  or  thirty  olfactory  nerves.^^  The  nerves,  after  enter- 
ing the  nasal  fossa  through  the  cribriform  plate,  are  distrib- 
uted to  the  Schneiderian  membrane.  The  cells  of  Max 
Schultze  in  the  Schneiderian  membrane  are  the  real  cell- 
bodies  of  the  olfactory  nerve  fibers  (axones),  hence  the  latter 
grow  upward  to  the  bulb.  The  fibers  form  the  first  layer  of 
the  bulb,  olfactory  nerve  layer,  and  arborize  about  the  den- 
drites of  the  large  mitral  cells  to  form  the  second  layer, — 
the  stratum  glomerulosum.  In  the  third  layer  of  the  gray 
matter  are  found  great  mitral  cell-bodies,  whose  medullated 
axis-cylinders,  or  axones,  form  the  white  matter  of  the  bulb ; 
and,  continued  backward,  constitute  the  olfactory  tract. 

Olfactory  Tract. — The  tract^*  is  triangular  in  section, 
nearly  an  inch  long  and  one  line  in  width.  It  is  concealed 
in  the  olfactory  sulcus.  At  its  base  it  divides  into  external 
and  infernal  root,^^  which  inclose  between  them  the  trigone 
into  which  some  fibers  may  be  traced,  forming  the  middle 
root.^^  The  external  root  courses  backward  and  outward  and 
terminates  in  the  uncus  at  the  anterior  extremity  of  the  hip- 
pocampal  convolution.  It  crosses  the  anterior  perforated 
space.  The  internal  root  bends  sharply  inward,  toward  the 
median  line,  and  runs  between  the  trigone  and  area  of  Broca. 
Its  fibers  turn  into  Broca^s  area  and  the  gyrus  fomicatus. 
Thus  the  two  roots  unite  the  opposite  ends  of  the  limbic  lobe. 
From  the  bifurcation  of  the  olfactory  tract,  a  few  fibers  pro- 
ceed into  the  trigone  and  frontal  lobe. 

(63)  Nervi   olfactorii. 

(64)  Tractus   olfactorius. 

(65)  Striae  olfactorise,   lateralis,   medialis,   intermedia. 


24  THE    BRAIN   AND   SPINAL    CORD. 

The  Trigone  and  Area  of  Broca. — The  triangular  portion 
of  coi-tex  between  the  inner  and  outer  olfactory  roots,  called 
the  trigone,^^  is  continuous  medially  with  Broca's  area.^''' 
The  internal  root  marks  the  boundary  between  them.  Both 
are  bounded  behind  by  the  fissura  prima  (transverse  part), 
and  the  oblique  part  of  the  same  fissure  separates  the  area 
of  Broca  from  the  peduncle  of  the  corpus  callosum.  The 
area  of  Broca  is  limited  in  front  by  a  slight  curved  depres- 
sion, the  fissura  serotina.  On  the  medial  surface,  Broca's 
area  joins  the  gyrus  fornicatus. 

Some  of  the  fibers  of  the  middle  root  of  the  olfactory  tract 
probably  pass  through  the  anterior  commissure;  and,  after 
piercing  the  opposite  corpus  striatum,  terminate  in  the  tem- 
poral lobe.  They  constitute  the  only  olfactory  decussation 
known. 

The  Posterior  Offactory  Lohule  is  identical  with  the  ante- 
rior perforated  lamina.^ ^  It  is  separated  from  the  trigone  by 
the  transverse  fissura  prima.  Internally,  it  is  in  direct  con- 
tinuity with  the  lamina  cinerea.  The  optic  tract  bounds  it, 
postero-medially.  Externally,  it  forms  the  floor  of  the  valle- 
cula Sylvii,  where  it  is  overlapped  by  the  temporal  lobe.  Su- 
periorly, it  is  continuous  with  the  base  of  the  corpus  striatum. 
Coursing  over  the  inner  and  outer  border  of  the  anterior  per- 
forated lamina  are  the  callosal  peduncle  and  external  ol- 
factory root,  which  converge  and  meet  in  the  hippocampal 
convolution.  The  perforations  of  the  lamina  are  for  the 
antero-lateral  ganglionic  arteries. 

Section  II. — Interior  Surface  of  the  Cerebrum. 

The  boundaries  of  the  cerebral  ventricles  constitute  the 
interior  surface  of  the  cerebrum.     Considering  all  the  cere- 

(66)  Trigonum  olfactorium. 

(67)  Area  parolfactoria  (Broca). 

(68)  Lamina  perforata  anterior. 


THE    CEREBRUM.  2$ 

bral  cavities  together,  we  notice  that  they  occupy  a  wedge- 
like space.  In  shape  the  wedge  is  rectangular;  and  it  stands, 
base  upward,  against  the  corpus  callosum.  Its  beveled  sur- 
faces look  toward  the  hemispheres.  The  blade  is  driven  down- 
ward as  if  to  split  the  cerebrum  into  lateral  halves,  the  edge 
resting  on  the  medial  structures  at  the  base  of  the  brain. 
The  space  is  inclosed  laterally  between  the  diverging  internal 
capsules,  which,  within  the  hemispheres,  decussate  with  the 
lateral  extremities  of  the  corpus  callosum.  The  two  struc- 
tures most  necessary  to  an  understanding  of  the  cerebral 
cavity,  therefore,  are  the  internal  capsule^  and  corpus  cal- 
losum. ' 

Internal  Capsule. — Looking  at  the  base  of  the  brain,  we 
see  two  broad  bands  of  nerve  fibers,  the  crustae,^  issue  from  the 
front  of  the  pons  and,  diverging  upward  and  forward,  enter 
the  hemispheres  beneath  the  optic  tracts.  These  peduncular 
fibers  are  reinforced  by  additional  fibers  within  the  hemi- 
sphere. The  fibers  then  radiate  toward  the  cerebral  cortex 
in  the  form  of  a  hollow  cone  or  funnel.  This  funnel-like 
group  of  fibers  is  the  internal  capsule.  The  bell  of  the  fun- 
nel opens  upward  and  outward  and  contains  the  lenticular 
nucleus;  its  solid  spout,  directed  toward  the  pons  and  me- 
dially, is  the  crusta.  Antero^inferiorly  the  fibers  in  the  bell 
of  the  funnel  diverge  to  opposite  sides  of  the  fissure  of  Syl- 
vius and  produce  a  break  in  its  continuity,  the  hiatus  8ylvii; 
otherwise  the  funnel  is  complete.  As  the  internal  capsule 
proceeds  into  the  hemisphere,  it  impales  the  corpus  striatum 
in  such  manner  as  to  place  the  caudate  nucleus  and  amygdala 
upon  its  circumference  and  to  inclose  within  its  walls  (to 
capsulate)  the  lenticular  nucleus.  The  lenticular  nucleus  is 
separated  externally  from  the  claustrum  by  a  thin  layer  of 
fibers  called  the  external  capsule.^ 

(1)    Capsula  interna.    (2)    Bases  pedunculi.     (3)    Capsula  externa. 


26  THE    BRAIN    AND    SPINAL    CORD. 

Inferior  Lamina. — -Tlie  internal  capsule*  is  flattened  from 
above  downward.  It  has,  therefore,  a  superior  and  an  infe-: 
rior  lamina,  which,  posteriorly,  are  continuous  with  each- 
other;  but,  anteriorly,  are  separated  by  the  fissure  of  Sylvius.: 
The  inferior  lamina  (or  inferior  ramus,  as  seen  in  sagittal/ 
section)  is  a  very  thin  layer  and  bevels  down  to  a  sharp  edge: 
anteriorly.  In  front  it  presents  a  free  border.  Its  fibers 
pass  outward  beneath  the  lenticular  nucleus  and,  after  wind- 
ing over  the  amygdala  and  the  descending  horn  of  the  lateral 
ventricle,  terminate  in  the  parietal  and  temporal  lobes. 

Motor  Fibers. — It  contains  part  of  the  Temporo-pontal 
motor  tract  which  extends  from  the  temporal  cortex  to  the 
nucleus  of  the  pons. 

Sensory  Fibers. — ^And  also  the  following  sensory  fibers 
are  found  in  the  inferior  lamina,  viz.,  the  Ansa  Peduncularis 
(conraionl  sensory)  running  from  the  thalamus  to  the  som- 
sesthetic  cortex,  and  part  of  the  Aciistic  Eadiations  (special 
sensory)  which  ext^snd  from  the  internal  geniculate  body 
to  the  auditory  cortex  in  the  superior  and  transverse  tem- 
poral gyri.  In  the  angle  between  the  descending  horn  and 
the  body  of  the  lateral  ventricle,  the  inferior  lamina  joins 
the  superior. 

The  Superior  Lamina  (or  superior  ramus)  of  the  internal 
capsule  contains  most  of  the  crusta.  It  is  a  thick  and  strong 
sheet  of  fibers.  Often  it  is  considered  as  identical  with  the 
"internal  capsule,'^  the  inferior  lamina  being  disregarded. 
The  superior  lamina  ascends,  fan-like,  from  the  crusta  to  the 
lateral  extremity  of  the  corpus  callosum,  with  which  it  in- 
tercrosses. It  has  a  free  border  anteriorly,  though  imbedded 
in  the  corpus  striatum.  Upon  its  internal  surface  rest  the 
optic  thalamus,  below  and  behind,  and  the  caudate  nucleus, 
above  and  farther  forward.  It  thus  separates  the  optic  thala- 
(4)    Capsula  Interna.  '  .   :^    i   : 


THE   CEREBRUM  2/ 

mus  and  caudate  nucleus  from  the  lenticular  nucleus.  A 
bend  near  the  middle  of  the  superior  lamina,  called  the 
genUj  divides  it  into  an  anterior^  and  a  posterior  segment,^ 
which  tend  slightly  outward  from  the  genu  and  form  an  angle 
with  each  other,  open  outward,  of  about  120  degrees. 

Motor  Fibers. — The  fibers  of  the  genu  of  the  internal  cap- 
sule are  very  largely  motor  and  constitute  the  Pyramidal 
Tract.  They  may  be  traced  from  the  Eolandic  area  of  the 
cortex,  through  the  genu  of  the  internal  capsule  and  middle 
three-fifths  of  the  crusta,  and  on  down  into  the  spinal  cord, 
where  they  end  in  ramifications  about  the  cell-bodies  in  the 
anterior  horn  of  gray  matter.  From  these  same  spinal  cell- 
bodies  other  fibers  rise  which  constitute  the  motor  part  of  the 
spinal  nerves.  Fibers  of  the  pyramidal  tract  also  end  in  the 
mid-brain  pons  and  medulla:  their  end-tufts  are  related  to 
the  nuclear  cell-bodies  of  motor  cranial  nerves.  The  anterior 
segment  (pars  frontalis)  of  the  internal  capsule  contains  a 
motor  tract  which  extends  from  the  prefrontal  cortex  through 
the  inner  one^fifth  of  the  crusta  to  the  nucleus  of  the  pons 
and  motor  nuclei  of  cranial  nerves  (Flechsig).  It  is  the 
Fronto-pontal  Tract."^  In  the  posterior  segment  (pars  occipi- 
talis), behind  the  pyramidal  tract,  and  also  partly  in  the 
inferior  lamina,  is  another  motor  tract,  described  by  Flechsig. 
It  rises  from  the  temporal  cortex  and  running  beneath  and 
behind  the  lenticular  nucleus  and  through  the  outer  one-fifth 
of  the  crusta,  terminates  in  the  nucleus  of  the  pons,  and  also 
in  nuclei  of  motor  cranial  nerves  (Spitzka).  That  is  the 
Temporo-pontal  Tract.^ 

Sensory  Fibers. — In  both  segments  of  the  internal  capsule 
there  are  oommon  sensory  fibers  which  rise  chiefly  in  the 

(5)  Pars  frontalis. 

(6)  Pars  occipitalis. 

(7)  Traotus  cerebro-corticopontalis  frontalis. 

(8)  T.   cerebro-corticopontalLs  temporalis. 


28  THE    BRAIN   AND    SPINAL    CORD. 

optic  tlialamus  and  end  in  the  somaesthetic  cortex.  They 
constitute  the  Cortical  Fillet  and  convey  ordinary  sensations. 
In  the  anterior  segment  is  the  Anterior  Stalk  of  the  Thal- 
amus which  ends  in  somaesthetic  cortex  anterior  to  the  pre- 
central  fissure.  The  posterior  segment  contains  the  Ansa 
Lenticularis,  which  conveys  ordinary  sensations  from  the 
thalamus  to  the  somaesthetic  cortex  chiefly  in  the  upper  Eo^ 
landic  area.  At  the  junction  of  the  superior  and  inferior 
laminsB  of  the  internal  capsule  are.  the  special  sense  fibers. 
The  Optic  Eadiations^  and  Auditory  Eadiations^^  occupy  the 
retro-lenticular  part  of  the  internal  capsule.  The  former  ex- 
tend through  it  from  the  optic  thalamus  and  external  genicu- 
late body  to  the  cuneus;  the  latter  rise  in  the  internal  genic- 
ulate body  and  end  in  the  superior  and  transverse  temporal 
convolutions.  Many  fibers  of  the  internal  capsule  give  off 
branches  (collaterals)  which  pass  through  the  corpus  callo- 
sum  to  the  opposite  hemisphere;  other  fibers  may  be  traced 
entire  through  the  same  course  to  the  cortical  cells  of  the  op- 
posite side.     (For  fibers  of  inferior  lamina  see  page  26.) 

The  superior  lamina  of  the  internal  capsule,  proceeding 
outward  and  upward  into  the  hemisphere,  decussates  with 
the  corpus  callosum  and  enters  into  the  corona  radiata.  To- 
gether with  the  caudate  nucleus,  optic  thalamus  and  tsenia 
semicircularis,  which  lie  on  its  internal  surface,  it  forms  the 
entire  lateral  boundary  of  the  general  cavity  of  the  cerebrum. 
It  thus  determines  the  lateral  part  of  the  interior  cerebral 
surface. 

Corpus  Callosuin. — The  entire  roof  of  the  cerebral  cavity, 
representing  the  base  of  the  wedge,  is  formed  by  the  corpus 
callosum.  A  part  of  the  anterior  boundary  is  also  formed 
by  it.     The  corpus  callosum  is  a  thick  sheet  of  fibers  four 

(9)  Radiatio   occipito-thalamica   (Gratioleti). 

(10)  Radiatio  temporothalamica. 


THE    CEREBRUM.  29 

inches  broad,  from  before  backward,  which  joins  the  hemi- 
spheres together.  It  constitutes  the  great  white  commissure, 
being  composed  chiefly  of  those  medullated  cortical  axones 
which  end  in  arborizations  about  cortical  cells  of  the  opposite 
hemisphere.  It  contains  some  fibers  which,  after  passing 
through  it,  turn  down  in  the  internal  capsule;  and,  also,  col- 
laterals from  capsular  and  association  fibers.  The  corpus 
callosum  is  placed  nearer  to  the  anterior  than  the  posterior 
pole  of  the  hemispheres.  Separating  the  hemispheres  above, 
it  is  seen  in  the  bottom  of  the  great  longitudinal  fissure.  It 
is  about  an  inch  in  transverse  length. 

The  upper  surface  is  concave  from  side  to  side;  and  di- 
vided, medially,  by  a  longitudinal  raphe.  Transverse  striae 
are  plainly  visible.  A  few  longitudinal  stria  are  also  found 
running  on  either  side  of  the  raphe,  the  nerves  of  Lancisi^^ ; 
and  others  run  near  the  lateral  end  of  the  callosum.^  ^  At  the 
anterior  and  at  the  posterior  border,  the  corpus  callosum  is 
bent  downward  (scroll  like) ;  hence,  it  is  superiorly  convex 
from  before  backward. 

Its  inferior  surface  is  concave  antero-posteriorly  and  near 
its  posterior  border  is  fused  with  the  body  of  the  fornix. 
Anterior  to  that  fusion,  it  is  joined  to  the  fornix,  along  the 
median  line,  by  the  septum  lucidum. 

The  posterior  l order  is  flexed  downward  about  forty-five 
degrees.  Giving  passage  to  the  fibers  which  join  the  middle 
and  posterior  parts  of  the  hemispheres,  the  posterior  border 
is  the  thickest  part  of  the  corpus  callosum.  It  is  on  that  ac- 
count called  the  pad,  or  splenium. 

The  anterior  border  is  bent  downward  and  then  backward, 
sweeping  through  180  degrees  of  flexion.  It  terminates  in 
a  sharp  edge  (sharp  point,  seen  in  sagittal  section)  called  the 

(11)    striae  longitudinales  mediales  et  laterales. 


30  THE    BRAIN   AND   SPINAL    CORD. 

rostrum.  The  rostrum  is  continuous  with,  the  lamina  termi- 
nalis  at  the  base  of  the  brain.  It  sends  downward  on  either 
side  a  band  of  fibers,  continuous  with  the  nerves  of  Lancisi, 
which  constitutes  the  peduncle  of  the  corpus  callosum.  Each 
peduncle,  after  passing  across  the  anterior  perforated  lamina, 
ends  in  the  uncus  of  the  hippocampal  gyrus.  The  transverse 
fibers  of  the  rostrum,  in  the  hemisphere,  form  the  floor  of 
the  anterior  horn  of  the  lateral  ventricle. 

Genu  and  Truncus. — The  down-turned  part  of  the  corpus 
callosum  is  the  genu.  It  joins  the  rostrum  to  the  main  body, 
the  truncus.  The  genu  forms  part  of  the  anterior  boundary 
of  the  cerebral  cavity;  the  truncus  forms  the  roof.  Fibers 
uniting  the  frontal  lobes  of  the  'cerebrum  pass  through  the 
genu,  and  in  the  hemisphere,  bound  the  anterior  horn  of  the 
lateral  ventricles  above  and  in  front.  Those  fibers  arching 
forward  and  forming  the  roof  of  the  anterior  horn  are  called 
the  forceps  minor.  The  forceps  major,  composed  of  fibers 
from  the  splenium  which  bend  backward  into  the  occipital 
lobe,  lies  in  the  roof  and  inner  wall  of  posterior  horn. 

Each  lateral  extremity  of  the  corpus  callosum  is  overhung 
by  the  gyrus  fomicatus,  which  covers  the  lateral  longitudinal 
striae  (taeniae  tectae).^^  Inclosed  between  the  gyrus  fomicatus 
and  corpus  callosum  is  the  fissure-like  ventricle  of  the  callo- 
sum, which  represents  part  of  the  fissura  prima  of  the  embryo. 
Under  the  splenium  the  fissura  prima  is  continued  in  the  hip- 
pocampal fissure. 

The  boundaries  of  the  general  cavity  of  the  cerebrum  may 
be  given  as  follows: 

Roof  (base  of  wedge) — 
Corpus  callosum. 

(12)    striae   longitudinales  laterales. 


THE    CEREBRUM.  31 

Floor  (edge  of  wedge) — 
Tegmentum  (Mid-brain), 
Posterior  perforated  lamina  (Mid-brain), 
Tuber  cinerenm, 
Infundibulum, 

Lamina  cinerea.  ! 

Lateral  wall  (beveled  surface) — 
Internal  capsule. 
Caudate  nucleus. 
Taenia  semicircularis, 

Optic  thalamus.  ' 

Anterior  wall  (border  of  wedge) — 
Lamina  terminalis. 
Anterior  commissure. 

Genu  of  corpus  callosum.  ; 

Posterior  wall — 

Corpora  quadrigemina  (Mid-brain)  and 

Posterior  commissure  (with  aqueduct  of  Sylvius  beneath 

them). 
Pineal  body, 
Grreat  transverse  fissure,  containing  the  velum  interposi- 

tum, 
Splenium  (being  bent  down  slightly  behind  the  cavity). 
The  cerebral  cavity  thus  bounded  is  subdivided  by  two 
partitions.  The  body  of  the  fornix,  together  with  the  velum 
interpositum  and  roof  epithelium  of  the  third  ventricle,  forms 
a  horizontal  partition  which  divides  the  cavity  into  an  upper 
and  lower  chamber.  The  superior  chamber  is  divided  into 
two  lateral  chambers,  the  lateral  ventricles,  by  a  double  ver- 
tical partition,  the  septum  lucidum.  The  inferior  chamber 
is  the  third  ventricle. 


32  THE    BRAIN   AND   SPINAL   CORD. 

The  body  of  the  fornixes  jg  ^  triangular  sheet  of  fibers, 
whose  base  is  attached  to  the  under  surface  of  the  splenium 
of  the  corpus  callosum,  and  whose  bifid  apex  extends  forward 
to  the  rostrum  and  to  the  anterior  commissure.  Its  lateral 
borders  rest  on  the  optic  thalami,  the  velum  interpositum 
alone  intervening.  And  the  narrow  chamber  between  the 
optic  thalami  (the  third  ventricle)  is  separated  from  the 
broader,  superior  part  of  the  cerebral  cavity  by  the  body  of 
the  fornix.  The  bo^dy  of  the  fornix  is  produced  by  the  ap- 
proximation of  two  bundles  of  white  fibers,  one  belonging  to 
each  hemisphere.    These  bundles  are  the  pillars  of  the  fornix. 

The  posterior  pillar^^  may  be  traced  from  the  uncus  (as 
corpus  fimbriatum),  and  from  the  hippocampus  major,  its 
chief  origin,  upward  through  the  descending  horn  and  into 
the  floor  of  the  body  of  the  lateral  ventricle,  where  it  unites 
with  its  fellow  of  the  opposite  side  in  forming  the  body  of 
the  fornix.  At  the  apex  of  the  body  of  the  fornix,  which  is 
the  anterior  end,  the  bundles  again  separate  and  become  the 
anterior  pillars.  The  posterior  pillars  are  united  at  the  back 
part  of  the  body  of  the  fornix  by  a  few  transverse  and  oblique 
fibers  which  form  the  lyre,  or  commissura  hippocampi.  The 
commissure  is  best  seen  when  the  corpus  callosum  and  fornix 
are  viewed  from  below ;  its  fibers  connect  each  posterior  pillar 
of  the  fornix  with  the  optic  thalamus,  hippocampus  major 
and  uncus  of  the  opposite  side. 

The  anterior  pillars ^^  one  on  either  side,  pass  down  in  front 
of  the  optic  thalami,  bounding  the  foramina  of  Monro;  and 
then  descend  to  the  corpora  albicantia,  at  the  base  of  the 
brain.    On  the  way  down  the  pillars  pass  behind  the  anterior 

(13)  Corpus  fornicis. 

(14)  Crus   fornicis. 

(15)  Columnse  fornicis. 


THE    CEREBRUM.  33 

commissure,  beyond  which  each  pierces  the  inner  part  of  the 
optic  thalamus  of  the  same  side.  The  fibers  of  the  anterior 
pillars  probably  terminate  in  the  corpora  albicantia,  from 
which  other  fibers  take  their  origin  (the  bundles  of  Vicq 
d^Azyr)^^  and  ascend  to  the  anterior  nuclei  of  the  optic 
thalami. 

The  up'per  surface  of  the  body  of  the  fornix  is  convex 
from  before  backward.  It  forms  the  postero-median  part  of 
the  floor  of  the  lateral  ventricle.  Medially,  it  is  joined  to  the 
corpus  callosum  by  the  septum  lucidum.^"^ 

The  septum  lucidum,  a  double-walled  sagittal  partition, 
divides  the  superior  chamber  of  the  cerebral  cavity  into  lateral 
halves,  the  lateral  ventricles.  The  septum  lucidum  is  cres- 
centic  in  outline.  Its  convex  border  fits,  medially,  into  the 
concave  surface  of  the  body,  genu  and  rostrum  of  the  corpus 
callosum.  Its  concave  border  rests  upon  the  fornix.  Each 
wall  of  the  septum  lucidum  is  a  part  of  the  original  medial 
wall  of  the  cerebral  hemisphere  and  is,  therefore,  composed 
of  cortical  and  medullary  matter.  The  walls  inclose  a  part 
of  the  great  longitudinal  fissure,  called  the  fifth  ventricle. 
That  fissure,  in  embyro,  was  open  down  to  the  velum  inter- 
positum  on  the  inter-brain;  but  its  lower  part  becomes  cut 
off  and  inclosed  by  the  development  of  the  fornix,  anterior 
commissure  and  corpus  callosum.  The  cerebral  cavity  is 
thus  divided  into  four  ventricles,  viz. : 

Two  lateral  (the  ventricles  of  the  hemispheres), 

Fifth  (the  ventricle  of  the  great  longitudinal  fissure),  and 

Third  (ventricle  of  the  inter-brain). 

THE   FIFTH   VENTRICLE. 

This  is  the  fissural  ventricle,  or  the  ventricle  of  the  sep- 

(16)  Fasciculus   thalamo-mamlllarls. 

(17)  Septum  pellucidum,  ,  ,  J 


34  THE    BRAIN    AND    SPINAL    CORD. 

tum.^^  The  fifth  ventricle  is  a  very  narrow,  anteroposterior 
cleft  between  the  walls  of  the  septum  lucidum,  with  which 
it  coincides  in  extent.  It  is  situated  within  the  concavity  of 
the  corpus  callosum  between  the  lateral  ventricles,  above  and 
anterior  to  the  third  ventricle.  Below  and  posteriorly  it  is 
bounded  by  the  fornix.  It  is  not  a  part  of  the  embryonic 
brain  cavity,  but  of  the  great  longitudinal  fissure.  There- 
fore it  does  not  communicate  with  any  other  ventricle,  each 
of  the  others  being  a  part  of  the  cavity  of  the  neural  tube 
from  which  both  brain  and  cord  are  developed.  Instead  of 
ependyma,  which  lines  other  ventricles,  the  lining  of  the 
fifth  is  modified  pia  mater.     A  lymph-like  fluid  fills  it. 

THE   LATERAL  VENTRICLE. 

The  hemispheres  contain  the  largest  of  the  six  ventricles. 
Situated  one  on  either  side  of  the  median  line,  the  ventricles 
of  the  hemispheres  are  very  naturally  called  the  lateral 
ventricles.i^  Each  represents  a  branch  of  the  cavity  of  the 
embryonic  neural  tube.  In  consequence,  the  lateral  ventricles 
communicate  with  all  others  except  the  fifth.  By  the  fora- 
men of  Monro,  each  directly  communicates  with  the  third 
ventricle;  and  through  that,  indirectly,  with  the  fourth  and 
sixth.  The  foramen  of  Monro^o  is  situated  between  the  front 
of  the  optic  thalamus  and  the  anterior  pillar  of  the  fornix. 
It  extends  between  the  anterior  extremity  of  the  third  ven- 
tricle (the  aula)  and  the  junction  of  the  anterior  horn  with 
the  body  of  the  lateral  ventricle.  The  lateral  ventricles  are 
lined  with  ependyma,  which  is  a  transparent  membrane  com- 
posed of  two  layers,  viz.,  neuroglia,  with  a  covering  of 
columnar  ciliated  epithelial  cells.     Over  the  optic  thalamus 

(18)  Cavum  septl  pellucldl. 

(19)  Ventriculi  laterales. 

(20)  Foramen    interventriculare    (Monroi). 


THE    CEREBRUM.  35 

(the  part  seen  in  the  lateral  ventricle)  and  the  choroid  plexus, 
the  neurogliar  layer  is  absent. 

The  lateral  ventricle  may  be  studied  best  in  four  parts: 
the  central  part  or  body ;  the  anterior,  the  middle  or  descend- 
ing, and  the  posterior  comu. 

The  body  of  the  lateral  ventricle^i  is  the  ventricle  of  the 
parietal  lobe  of  the  cerebrum.  The  following  are  its  bound- 
aries : 

Eoof — Corpus  callosum. 

Floor  (from  before,  backward  and  inward) — 
Caudate  nucleus  of  the  corpus  striatum. 
Taenia  semicircularis. 
Optic  thalamus  (covered  by  epithelium). 
Choroid  plexus  (covered  by  epithelium), 
Fornix. 

Medial  wall — Septum  lucidum. 

External  wall — Internal  capsule. 

The  corpus  callosum  forms  a  complete  roof  for  the  body 
of  the  lateral  ventricle.  The  roof  inclines  upward  and  out- 
ward from  the  septum  lucidum,  the  inner  wall  of  the  ven- 
tricle, to  the  superior  lamina  of  the  internal  capsule,  which 
forms  its  outer  wall.  The  floor  of  the  body  of  the  ventricle 
is  formed  by  the  five  parts,  as  named  above,  which  will  now 
be  considered  in  the  order  given. 

Corpus  Striatum. — The  striated  body  is  the  basal  ganglion 
of  the  hemisphere.  It  is  an  ovoid  mass  of  gray  matter  im- 
bedded, for  the  most  part,  in  the  cerebral  medulla;  but  it  is 
continuous  below  with  the  anterior  perforated  lamina  and 
extends  above  into  the  floor  of  the  lateral  ventricle.  It  meas- 
ures two  inches  from  before  backward,  an  inch  and  a  quarter 
transversely,  and,  from  above  downward,  one  inch  and  a  half. 

(21)    Ventriculus  lateralis  (pars  centralis). 


36  THE    BRAIN    AND   SPINAL    CORD. 

It  is  placed  anterior  and  external  to  the  optic  thalamus.  It 
is  a  reddish-gray  body  and  the  streaked  appearance  of  the 
corpus  striatum  is  due  to  the  white  capsular  fibers  which 
pierce  it.  The  striated  body  is  an  important  way-station  in 
the  motor  conduction  path  and  perhaps  one  of  less  impor- 
tance in  the  sensory  path.  The  internal  capsule  divides  it 
into  two  nu.clei,  namety,  the  lenticular  nucleus  (extra ven- 
tricular part)  ,22  and  the  caudate  nucleus,  which  is  seen  in 
the  lateral  ventricle.  Anterior  to  the  free  borders  of  the 
superior  and  inferior  capsular  laminae,  the  two  nuclei  are 
united  with  each  other,  with  the  anterior  perforated  lamina 
and  with  the  lower  end  of  the  claustrum. 

The  Lenticular  Nucleus  occupies  the  cone-like  cavity  of  the 
internal  capsule,  by  whose  laminae  it  is  separated  from  the 
ventricle.  It  is  shorter  fore  and  aft  than  the  caudate  nu- 
cleus. It  resembles  a  biconvex  lens  with  a  somewhat  thick- 
ened anterior  border,  when  viewed  in  horizontal  section.  In 
transverse  vertical  section  through  its  center,  it  is  triangular 
in  shape.  The  hypotenuse  and  base  are  formed,  respectively, 
by  the  superior  and  inferior  laminae  of  the  internal  capsule. 
The  external  capsule  forms  the  perpendicular  anid  separates 
the  lenticular  nucleus  from  the  claustrum.  The  latter  is  a 
thin  sheet  of  isolated  gray  matter,  found  just  medial  to  the 
island  of  Reil.  In  extent  and  position,  fore  and  aft,  the 
island  of  Eeil  and  lenticular  nucleus  coincide.  The  lenticu- 
lar nucleus  is  subdivided  by  two  white  laminae,  parallel  with 
its  external  surface,  into  three  zones.  The  outer  zone,  called 
the  putamen,  is  deeply  pigmented,  and,  like  the  caudate 
nucleus,  is  of  a  reddish-gray  color;  but  the  two  inner  zones, 
having  less  pigment,  are  of  a  pale  yellowish  tint.  They  form 
the  globus  pallidum. 

The  Nucleus  Caudatus  (the  tailed  nucleus)  is  a  pear-shaped 

(22)    Nucleus  lentiforxnls. 


THE    CEREBRUM.  37 

body  of  reddisli-gray  color,  situated  on  the  perimeter  of  the 
internal  capsule.  It  is  the  intra- ventricular  part  of  the 
striated  body  and  forms  a  strip  of  the  ventricular  floor  along 
the  outer  wall.  The  hulh^^  of  the  caudate  nucleus  is  directed 
forward.  It  is  seen  in  the  anterior  horn  of  the  lateral  ven- 
tricle. From  the  bulb  the  nucleus  tapers  as  it  proceeds  back- 
ward through  the  body  of  the  ventricle.  Its  tail,  or  sur- 
cingle,^'^ turns  downward  in  the  roof  of.  the  middle  horn,  and 
ends  in  a  considerable  swelling,  called  the  amygdalaj^^  near 
the  apex  of  the  horn.  The  caudate  nucleus  is  covered  on  its 
ventricular  surface  by  ependyma.  The  opposite  surface, 
resting  against  the  fibers  of  the  internal  capsule,  is  irregular 
and  serrated. 

The  Taenia  Semicircularis^^  lies  just  internal  to  the 
nucleus  caudatus.  It  is  a  band  of  white  fibers  traversing  the 
floor  of  the  body  of  the  ventricle  and  the  roof  of  its  descend- 
ing horn,  but  covered  by  the  vein  of  the  striate  body.  It  may 
be  said  to  rise  from  the  amygdala.  Ascending  to  the  ventricle, 
it  passes  forward  between  the  caudate  nucleus  and  the  optic 
thalamus  to  the  foramen  of  Monro,  where  it  divides  into 
two  bundles.  One  of  them  joins  the  anterior  pillar  of  the 
fornix.  The  other,  passing  over  the  anterior  commissure, 
terminates  in  front  of  it  in  a  mass  of  cells  between  the  septum 
lucidum  and  the  nucleus  caudatus.  Perhaps  some  fibers 
terminate  in  the  latter. 

Optic  Thalinus.27 — A  fusiform  part  of  this  ganglion  of 
the  inter-brain  is  visible  in  the  floor  of  the  lateral  ventricle, 
between  the  taenia  semicircularis  and  the  choroid  plexus.  It 
extends  throughout  the  ventricular  body  from  the  foramen 
of  Monro  to  the  descending  horn.     A  transparent  layer  of 

(23)  Caput  nuclei  caudatl.  (26)    Stria  terminalis. 

(24)  Cauda  nuclei  caudati.  (27)    Thalamus. 

(25)  Nucleus  amygdalse. 


38  THE    BRAIN   AND    SPINAL    CORD. 

epithelium,  extending  from  the  fornix  to  the  tsenia  semi- 
circularis,  and  representing  the  hemisphere  wall,  covers  it. 
The  optic  thalamus  will  be  described  with  the  third  ventricle 
and  inter-brain. 

The  Choroid  Plexuses  of  the  lateral  ventricle  is  the  vascular 
border  of  the  velum  interpositum.  It  projects,  laterally,  from 
beneath  the  fornix  and  its  posterior  pillar  into  the  floor  of 
the  body  of  the  ventricle  and  the  inner  wall  of  the  descending 
horn.  The  epithelium,  above  mentioned,  invests  it;  and  it 
borders  the  fornix  like  a  ruffle.  It  is  called  choroid  plexus 
(chorion^  a  membrane)  because  it  is  membrane-like.  The 
anterior  choroid  artery^^  from  the  internal  carotid  and  the 
postero-lateral  choroid,  a  branch  of  the  posterior  cerebral,  sup- 
ply the  plexus.  The  former  pierces  the  temporal  lobe  and  en- 
ters the  apex  of  the  descending  horn  of  the  ventricle;  the 
latter  passes  in  through  the  great  transverse  and  choroid 
fissures,  following  the  velum  interpositum.  The  choroid  vein 
carries  the  blood  away.  At  the  foramen  of  Monro,  it  is  joined 
by  the  vein  of  the  striated  body  and  forms  the  vein  of  Galen. 
The  vein  of  Galen^^  courses  backward  in  the  velum  inter- 
positum and  unites  with  its  fellow  of  the  opposite  side;  and 
then  the  common  vein  of  Galen,^^  uniting  with  the  inferior 
longitudinal  sinus,  forms  the  straight  sinus. 

The  floor  of  the  body  of  the  lateral  ventricle  is  completed 
by  the  superior  surface  of  the  fornix. 

The  comua^^  Qf  i}^q  lateral  ventricle  are  three  in  number. 

The  anterior  cornu^^  projects  from  the  body  of  the  ven- 
tricle forward  and  outward  around  the  bulb  of  the  caudate 

(28)  Plexus  choroideus  ventriculi  lateralis. 

(29)  Arteiia  choroidea  anterior. 

(30)  Vena  cerebri  interna. 

(31)  V.   cerebri  magna  (Galeni). 

(32)  Cornua  ventriculi  lateralis. 

(33)  Cornu  anterius  ventriculi  lateralis. 


THE    CEREBRUM.  39 

nucleus.  It  is  the  ventricle  of  the  frontal  lobe  and  is  deep 
and  narrow.    Its  boundaries  are  as  follows: 

Koof — Corpus  callosum  (forceps  minor). 

Floor — ^Eostrum. 

Anterior  wall — Genu. 

Inner  wall — Septum  lucidum. 

Outer  wall — Caudate  nucleus. 

The  posterior  cornu^*  is  directed  backward  and  downward 
in  a  curve  concave  inward,  from  the  ventricular  body  into 
the  occipital  lobe.  Its  extremity  bends  medially  toward  the 
calcarine  fissure,  with  which  the  horn  is  parallel.  That  fissure 
produces  the  ridge  along  the  inner  wall  called  the  hippo- 
campns  minor.^^  The  posterior  horn  is  roofed  over  by  fibers 
from  the  splenium  of  the  corpus  callosum,  which  turn  down 
outside  the  horn  and  also  form  part  of  the  external  boundary. 
A  well-marked  bundle  of  fibers  from  the  splenium,  forceps 
major,  is  found  passing  along  the  medial  border  of  the  roof 
into  the  occipital  lobe.  The  white  matter  of  the  occipital 
lobe  forms  the  remaining  boundaries.  The  anterior  extrem- 
ity of  the  posterior  cornu  is  continuous,  laterally,  with  the 
beginning  of  the  descending  horn.  At  the  junction  of  the 
two  is  a  triangular  area,  the  trigonum  ventriculi. 

The  middle,  or  descending,  cornu^^  is  the  ventricle  of  the 
temporal  lobe.  Its  course  is  crescentic  as  it  follows  the  peri- 
meter of  the  internal  capsule.  It  first  runs  outward  arid 
backward  from  the  body  of  the  ventricle,  then  it  turns  down- 
ward, and  finally  it  proceeds  forward  and  inward  to  within 
an  inch  of  the  apex  of  the  temporal  lobe.  In  horizontal  sec- 
tion just  below  the  general  cavity  of  the  ventricle,  the  de- 
scending horn  is  triangular.  In  that  position  it  has  a  poste- 
rior wall  or  floor,  an  inner  wall,  and  a  curved  antero-external 

(34)  Cornu  posterius  ventriculi  lateralis. 

(35)  Calear  avis. 

(36)  Cornu   inferius   ventriculi   lateralis. 


40  THE    BRAIN    AND    SPINAL    CORD. 

wall  or  roof,  which  is  continuous  above  with  the  outer  wall 
and  floor  of  the  body  of  the  ventricle. 

The  parts  found  in  the  walls  of  the  descending  comu  may 
be  enumerated  as  follows : 

Eoof  (or  antero-extemal  wall) — 

Pulvinar  of  optic  thalamus  (covered  by  epithelium). 
Inferior  lamina  of  internal  capsule,  partially  covered 
by  surcingle  and  amygdala  of  caudate  nucleus,  and 
taenia  semicircularis. 
Floor  (or  posterior  wall) — 
Eminentia  collateralis, 
Hippocampus  major  and  pes  hippocampi, 
Posterior  pillar  of  fornix  and  corpus  fimbriatuni. 
Inner  wall  (medial) — 

Epithelium  (of  hemisphere  wall)  covering, 
Pulvinar, 
Choroid  plexus, 
Choroid  fissure,  and 
Dentate  fascia. 
The  structures  in  the  roof  of  the  descending  horn  have 
been  sufficiently  described.    They  are  easily  understood  when 
it  is  recalled  that  the  roof  of  the  horn  is  continuous  with  the 
outer  wall  and  floor  of  the  ventricle;  the  internal  capsule 
(inferior  lamina),  the  surcingle  and  amygdala  and  the  taenia 
semicircularis  form  it. 

Beginning  at  the  trigonum  ventricuW^  and  extending 
along  the  outer  border  of  the  floor  to  the  end  of  the  descend- 
ing horn  is  a  low  ridge  caused  by  the  collateral  fissure.  It 
is  the  eminentia  collateralis.  In  front  of  it  and  internal  to 
it  is  a  prominent  ridge,  the  hippocampus  major,^^  which  en- 

(37)  Trigonum  collaterale. 

(38)  Hippocampus. 


THE    CEREBRUM.  4I 

larges  downward  to  a  lobulated  extremity,  called  the  pes 
hippocampi.^^  Tlie  ridge  is  due  to  the  infolding  of  the  floor 
over  the  hippocampal  fissure  on  the  medial  surface  of  the 
cerebrum.  The  ventricular  surface  of  the  hippocampus 
major  is  formed  by  a  lamina  of  white  matter,  the  alveus,  but 
the  deeper  part  is  cortical  matter  composed  almost  entirely 
of  pyramidal  cell-bodies.  The  posterior  pillar  of  the  fornix 
rests  in  the  concavity  of  the  hippocampus,  where  most  of  its 
fibers  originate,  but  a  small  bundle  of  them,  the  corpus 
flmbriatum,  passes  beyond  it  to  its  origin  in  the  uncus. 

A  layer  of  epithelium,  representing  the  hemisphere  wall, 
forms  the  floor  of  the  choroid  fissure  and  the  whole  inner 
wall  of  the  descending  cornu.  It  covers  the  cushion-like 
projection  (the  pulvinar)  of  the  optic  thalamus,  which  forms 
a  small  part  of  both  roof  and  inner  wall.  Behind  and  su- 
periorly, it  is  attached  to  the  pillar  of  the  fornix,  from  which 
it  extends  forward  and  outward  to  the  taenia  semicircularis. 
The  epithelium  covers  the  choroid  fissure,  which  otherwise 
would  form  a  communication  between  the  horn  and  the 
exterior.  Through  the  choroid  fissure  the  border  of  the 
velum  interpositum  projects  toward  the  ventricle,  and,  push- 
ing the  epithelium  before  it  into  the  horn,  forms  the  choroid 
plexus.  Within  the  fissure  there  is  a  serrated  free  border  of 
cortex  called  the  dentate  fascia^^  The  dentate  fascia  folds 
medially  in  front  of  the  hippocampal  fissure  and  with  the 
hippocampus  major  forms  an  S-shaped  fold  of  the  cortex. 
The  S-shape  is  perfect  in  the  left  hemisphere,  when  viewed 
with  the  frontal  lobes  upward  and  the  convex  surface  of  the 
brain  toward  the  spectator.  The  top  of  the  letter  is  the  fascia 
dentata;  the  superior  curve  is  the  hippocampus,  produced  by 

(39)  Digitationes   hippocampi. 

(40)  Fascia  dentata  hippocampi. 


42  THE    BRAIN   AND   SPINAL   CORD. 

the  hippocampal  fissure,  the  upper  concavity;  the  lower  con- 
cavity, open  toward  the  ventricle,  is  the  groove  between  the 
hippocampus  major  and  the  eminentia  collateralis. 

THE   THIRD   VENTRICLE   AND   INTER-BRAIN. 

The  inter-brain^i  is  medial  in  position.  It  is  situated 
beneath  the  fornix  and  the  layer  of  epithelium  extending 
from  the  border  of  the  fornix  to  the  taenia  semicircularis. 
The  velum  interpositum  only  intervenes  between  them. 
Laterally,  it  is  bounded  by  the  superior  laminae  of  the  in- 
ternal capsules.  The  ventricle  of  the  inter-brain  is  the 
third^^  iri  number.  The  third  ventricle,  therefore,  is  medi- 
ally located ;  and  is  at  a  lower  level  than  the  ventricles  of  the 
hemispheres.  Through  the  foramina  of  Monro,  its  anterior 
part  (the  aula)  communicates  with  each  lateral  ventricle,  and 
the  aqueduct  of  Sylvius  connects  it,  behind,  with  the  fourth 
ventricle.  The  thir^d  ventricle  is  fissure-like.  It  is  a  nar- 
row, vertical  cleft  about  an  inch  in  length  from  before  back- 
ward and  a  quarter  of  an  inch  broad  at  its  widest  part.  It 
separates  the  optic  thalami,  and  extends  almost  to  the  infe- 
rior surface  of  the  cerebrum.  The  roof  follows  the  curve 
of  the  fornix  and  arches  from  the  posterior  commissure  for- 
ward to  the  anterior  commissure.  The  anterior  wall  extends 
from  the  upper  border  of  the  anterior  commissure  down  to 
the  optic  recess,  at  the  angle  of  flexion  in  the  lamina  cinerea. 
The  -floor  describes  two  arches,  convex  toward  the  ventricle. 
The  first  arch,  very  convex  and  short,  stretches  between  the 
optic  recess  and  the  infundibulum,  in  which  the  floor  reaches 
its  lowest  point.  The  distance  from  the  infundibulum  to  the 
anterior  orifice  of  the  aqueduct  of  Sylvius  is  spanned  by  the 

(41)  Diencephalon. 

(42)  Ventriculus  tertius. 


THE    CEREBRUM.  43 

second  arch.  It  is  long  and  rather  flat.  Its  posterior  ex- 
tremity is  but  a  sixteenth  of  an  inch  below  the  posterior 
commissure;  the  anterior  orifice  of  the  Sylvian  aqueduct 
separates  them.  The  ventricle  is  thus  contracted  behind  to 
the  size  of  the  Sylvian  aqueduct,  with  which  it  is  continuous. 
The  lateral  walls  are  close  together  throughout.  At  one  point 
near  the  middle  they  come  together  and  are  joined  by  the 
gray,  or  middle,  commissure.^^  Antero-superiorly,  the 
lateral  wall  is  perforated  by  the  foramen  of  Monro.^*  That 
foramen  constitutes  the  slight  separation  between  the  front 
of  the  optic  thalamus  an!d  the  anterior  pillar  of  the  fornix. 
It  opens  into  the  lateral  ventricle  at  the  junction  of  the 
anterior  horn  with  the  body.  The  ependyma  which  lines  the 
third  ventricle  is  continuous  through  the  foramen  of  Monro 
with  the  lining  of  the  lateral  ventricle.  But  one  layer  of  the 
ependyma  is  present  in  the  roof  of  the  ventricle;  that  is  the 
epithelial  layer.  The  third  ventricle,  like  all  true  ventricles, 
is  occupied  by  cerebro^spinal  fluid. 

The  following  are  the  boundaries  of  the  third  ventricle : 
Roof- 
Posterior  commissure  and  commissura  habenlarum, 
Eoof  epithelium  and  pineal  body. 
Velum  interpositum  and  choroid  plexuses, 
Fornix. 
Anterior  wall — 

Epithelium,  covering 

Pillars  of  fornix  and  anterior  commissure. 
Lamina  terminalis. 
Floor — 

Lamina  cinerea  and  optic  conunissure, 

(43)  Massa  intermedia. 

(44)  Foramen  interventriculare. 


44  THE    BRAIN   AND   SPINAL    CORD. 

Tuber  cinereum  and  infimdibuliun, 

Corpora  albicantia, 

Posterior  perforated  lamina  (of  mid-brain). 

Tegmentum  (of  mid-brain). 
Posteriorly — 

Ventricle  is  continuous  with  aqueduct  of  Sylvius. 
Lateral  walls — 

Optic  thaJamus, 

Anterior  pillar  of  the  fornix,  and 

Foramen  of  Monro  between  them. 
Roof. — ^A  band  of  white  fibers  passes  across  the  back  part 
of  the  third  ventricle  and  supports  the  posterior  end  of 
the  roof  epithelium.  That  band  is  the  posterior  com- 
missure.*^ It  crosses  immediately  in  front  of  the  corpora 
quadrigemina.  Beneath  it  is  the  anterior  orifice  of  the 
aqueduct  of  Sylvius.  The  pineal  body  is  above  and  behind  it, 
and  the  commissure  is  inclosed  between  the  ventral  and  dorsal 
pineal  laminae.  The  posterior  commissure  stretches  from  one 
optic  thalamus  to  the  other;  but  most  of  its  fibers  terminate 
in  the  parieto-occipital  region.  It  contains  four  sets  of  fibers, 
viz. :  (1)  Commissural  fibers  between  the  optic  thalami  (  ?) ; 
(2)  the  upper  decussation  of  the  posterior  longitudinal 
bundles;  (3)  some  fibers  from  the  pineal  stria,  derived  from 
the  optic  tract  near  the  external  geniculate  body,  which  cross 
to  the  opposite  nucleus  (upper  part)  of  the  motor  oculi 
(Darkschewitsch) ;  and  (4)  fibers  from  the  fillet  crossing  to 
the  opposite  hemisphere. 

The  roof  epithelium  of  the  third  ventricle  stretches  from 
the  posterior  commissure  to  the  anterior  commissure  and 
laterally,  is  attached  to  the  upper  internal  border  of  the 
optic  thalamus.    It  is  the  supefrficial  layer  of  the  ependyma; 

(45)    Commissura  posterior. 


THE    CEREBRUM.  45 

but  it  is,  here,  the  only  adult  representative  of  the  roof  of  the 
neural  tube  (the  thalamencephalon) .  Anteriorly,  this  same 
epithelium  investing  the  anterior  commissure  and  pillars  of 
the  fornix,  is  the  only  representative  of  the  neural  wall 
(prosencephalon)  down  to  the  lamina  terminalis.  The  roof 
epithelium  presents  two  longitudinal  folds  suspenlded  in  the 
ventricle.  The  lower  layer  of  the  velum  interpositum,  con- 
stituting the  superior  choroid  tela/'^  invests  the  roof  epithe- 
lium of  the  third  ventricle  superiorly;  and,  dipping  down 
into  the  longitudinal  folds,  that  inferior  layer  of  the  velum 
interpositum  forms  the  choroid  plexuses'^^  of  the  third  ventri- 
cle, which  are  continuous  with  those  of  the  lateral  ventricles 
through  the  foramina  of  Monro.  At  the  back  part  in  the 
middle  line,  there  is  a  pouch-like  evagination  of  the  roof 
epithelium  in  the  embyro,  which  develops  into  the  pineal 
body. 

Pineal  Body,  or  Conarium. — It  is  a  cone-shaped  body,^^ 
a  quarter  of  an.  inch  high  and  one-sixth  of  an  inch  in  diam- 
eter. Joined  to  the  roof  of  the  third  ventricle  by  a  flattened 
stalk  or  peduncle.^ *^  It  is  also  called  the  epiphysis.  The 
pineal  body  is  situated  in  the  floor  of  the  great  transverse 
fissure,  directly  below  the  splenium  of  the  corpus  callosum, 
and  rests  between  the  superior  quadrigeminal  bodies  on  the 
dorsal  surface  of  the  mid-brain.  It  is  closely  invested  by  pia 
mater.  The  pineal  stalk  splits  into  a  dorsal  and  a  ventral 
lamina.  The  ventral  lamina,  passing  behind  the  posterior 
commissure,  disappears  beneath  it;  but  the  dorsal  stretches 
forward  over  the  commissure  in  continuity  with  the  roof 
epithelium.     The  borders  of  the   dorsal  lamina  are  thick- 

(47)  Tela  choroidea  ventriciili   tertil. 

(48)  Plexus   choroideus  ventrlculi   tertii. 

(49)  Corpus  pineale. 

(50)  Habenula. 


46  THE    BRAIN    AND   SPINAL    CORD. 

ened,  pineal  strise,^^  and  contain  fibers  which  are  derived 
from  the  anterior  pillar  of  the  fornix.  (Note  1,  add.,P.  225.) 
The  pineal  striae  aJso  contain  optic  fibers  which  pass  through 
the  posterior  commissure  to  the  nucleus  of  the  oculomotor 
nerve. 

The  interior  of  the  pineal  body  is  made  up  of  closed  fol- 
licles surrounded  by  ingrowths  of  connective  tissue.  The 
follicles  are  filled  with  epithelial  cells  mixed  with  calcareous 
matter,  the  brain-sand  (acervulus  cerebri).  Calcareous  de- 
posits are  found  also  on  the  pineal  stalk  and  along  the 
choroid  plexuses.  The  function  of  the  pineal  body  is  un- 
known. It  is  supposed  to  represent  a  cyclopian  eye.  In  the 
Hatteria,  a  New  Zealand  lizard,  it  projects  through  the 
parietal  foramen  and  presents  an  imperfect  lens  and  retina 
and,  in  its  long  stalk,  nerve  fibers. 

The  velum  interpositum,  a  double  triangular  fold  of  pia 
mater,  is  interposed  between  the  epithelium  of  the  third 
ventricle  and  the  medial  part  of  the  floor  of  the  two  lateral 
ventricles.  Its  apex  is  just  behind  the  anterior  commissure, 
and  its  base,  directed  backward,  is  continuous,  by  the  upper 
layer,  with  the  pia  of  the  occipital  lobes;  and,  by  the  inferior 
layer,  it  is  continuous  with  the  pia  on  the  dorsal  surface  of 
the  mid-brain  anld  cerebellum.  Each  border  constitutes  the 
choroid  plexus  of  the  lateral  ventricle,  and  is  seen  (through 
the  epithelium)  in  the  floor  of  its  body  and  along  the  inner 
wall  of  its  descending  horn.  The  inferior  lamina  of  the 
velum  interpositum  forms  the  superior  choroid  tela;^^  medi- 
ally it  invests  the  roof  epithelium  of  the  third  ventricle,  and, 
laterally,  it  covers  the  medial  half  of  the  upper  surface  of 
each  optic  thalamus.     It  forms  the  two  choroid  plexuses  of 

(51)  Stria  medullaris  thalami. 

(52)  Tela   choroidea  ventriculi  tertii. 


THE    CEREBRUM.  47 

the  third  ventricle,^^  which  depend  from  its  medial  portion. 
Between  the  inferior  and  superior  lamina  is  enclosed  some 
arachnoid  tissue;  and  the  veins  of  Galen  pass  back  through 
it  from  the  foramina  of  Monro  to  the  tentorium  cerebelli, 
where  they  join  with  the  inferior  longitudinal  sinus  in  form- 
ing the  straight  sinus. 

Anterior  Wall. — The  anterior  commissures^  is  a  very  dis- 
tinct round  bundle  of  white  fibers  about  an  eighth  of  an 
inch  in  diameter.  It  is  seen  in  the  anterior  wall  of  the  third 
ventricle  supporting  the  roof  epithelium.  The  epithelium 
there  bends  down  between  the  pillars  of  the  fornix  and  in- 
vests the  ventricular  surface  of  the  commissure.  The  an- 
terior commissure  rests  upon  the  upper  extremity  of  the 
lamina  terminalis,  between  the  pillars  of  the  fornix^,  behind, 
an^  the  rostrum  of  the  corpus  callosum,  in  front.  With  the 
last  two  structures  it  is  developed  from  the  hemisphere 
vesicles.  It  is  the  most  important  connecting  link  between 
the  hemispheres  in  vertebrates  withoxit  a  corpus  callosum  (all 
below  mammals).  Bending  shortly  backward  the  anterior 
commissure  pierces  the  inferior  part  of  the  globus  pallidus 
and  then  radiates  toward  the  cortex,  some  of  its  fibers  en- 
tering the  external  capsule.  It  contains  two  groups  of  fibers : 
(1)  the  anterior  group/^  which  is  the  commissure  of  the 
rhinencephalon,  called  the  pars  olfactoria;  and  (2)  the  pos- 
terior group,^^  the  pars  occipito-temporalis.  The  former 
connects  the  limbic  iobes  and  joins  each  to  the  opposite  olfac- 
tory tract;  the  latter  ends  in  the  inferior  part  of  the  occipital 
and  in  the  temporal  cortex.  In  man  it  is  larger  than  the  pars 
olfactoria.    The  upturned  part  of  the  lamina  cinerea,  called 

(53)  Plexus  choroideus  ventriculi  tertii. 

(54)  Commissura  anterior  (cerebri). 

(55)  Pars  anterior. 

(56)  Pars  posterior. 


48  THE    BRAIN   AND   SPINAL    CORD. 

lamina  terminalis,  extenlds  from  the  anterior  commissure  and 
rostrum  of  the  corpus  callosum  down  to  the  flexure  which 
incloses  the  optic  recess ;  it  completes  the  anterior  boundary  of 
the  third  ventricle. 

The  floor  is  very  narrow.  It  is  formed  by  the  interpedun- 
cular structures  plus  the  tegmentum,  namely :  lamina  cinerea 
(with  optic  chiasma  below  it),  tuber  cinereum  and  infundib- 
ulum,  corpora  albicantia,  posterior  perforated  lamina  and 
the  tegmentum.  The  last  two  are  the  middle  and  dorsal  por- 
tions of  the  mid-brain;  the  others  belong  to  the  inter-brain, 
and  all  extend  laterally  beneath  the  optic  thalami.  The  cor- 
pora albicantia,  located  on  either  side  of  the  median  line, 
may  be  excepted  from  the  ventricular  floor,  as  they  are  di- 
rectly beneath  the  thalami  (see  base  of  cerebrum). 

The  third  ventricle  has  its  lateral  wall  formed  by  the  optic 
thalamus  and  the  anterior  pillar  of  the  fornix.  The  pillar  of 
the  fornix,  diverging  from  its  fellow,  proceeds  downward  and 
backward  to  the  corpus  albicans  through  the  medial  part  of 
the  thalamus.  In  the  ventricle  it  is  covered  by  the  ependy- 
mal  epithelium.    It  bounds  the  foramen  of  Monro  in  front. 

Optic  Thalamus. — It  is  the  great  ganglion  of  the  inter- 
brain.  The  thalamus  (tJialamos,  a  bed)^"^  is  an  important 
sensory  way-station.  In  it  or  in  the  hypothalamic  nuclei 
almost  every  impulse  of  general  sensation,  in  its  journey  to 
the  cerebral  cortex,  is  transferred  to  a  higher  neurone.  The 
third  ventricle  separates  the  thalami  from  each  other,  ex- 
cept at  the  mid-point  where  they  are  joined  by  the  middle 
(gray)  commissure.^s  rp^g  thalamus  is  situated  behind  and 
medial  to  the  corpus  striatum,  and  projects  backward  over 
the  superior  surface  of  the  mid-brain.  Laterally,  it  rests 
against  the  superior  lamina  of  the  internal  capsule,  which 

(57)    Thalamus.  (58)    Massa  intermedia. 


THE    CEREBRUM.  49 

separates  it  from  the  lenticular  nucleus.  The  optic  thal- 
amus is  shaped  like  an  egg,  with  the  small  end  directed  for- 
ward. It  has  an  anterior  and  a  posterior  extremity  and  four 
surfaces:    Superior,  inferior,  internal  and  external. 

Extremities. — The  anterior  extremity  of  the  thalamus  is 
lost  in  a  large  group  of  fibers  (anterior  stalk)  which,  run- 
ning through  the  anterior  segment  of  the  internal  capsule, 
ends  in  the  gyrus  fornicatus  and  the  frontal  lobe  of  the 
cerebrum. 

The  posterior  end  presents  a  large  pillow-like  prominence, 
the  pulvinar;  and  beneath  it  is  a  smaller  swelling,  which 
forms  the  lowest  point  of  the  thalamus,  the  external  geni- 
culate body.  The  internal  geniculate  body  (of  the  mid- 
brain) is  also  continuous  with  this  extremity  internal  to  the 
pulvinar.  The  two  geniculate  bodies  constitute  the  meta- 
thalamus. 

Surfaces. — The  internal,  or  medial,  surface  of  the  optic 
thalamus  forms  the  lateral  wall  of  the  third  ventricle.  It 
is  joined  to  the  internal  surface  of  the  opposite  thalamus  by 
the  middle  commissure.  Both  this  and  the  superior  surface 
are  composed  of  a  thin  lamina  of  longitudinal  white  fibers, 
the  stratum  zonale. 

The  superior  surface  of  the  thalamus  is  divided  by  an 
oblique  groove,  the  choroid  groove,  corresponding  in  posi- 
tion to  the  border  of  the  fornix,  into  two  areas.  The  area 
inside  the  groove  is  covered  by  the  velum  interpositum  and 
the  fornix.  Internall}^  it  is  bounded  by  the  pineal  stria  and 
attachment  of  the  roof  epithelium.  Posteriorly,  next  the 
stria,  is  a  triangular  depression  bounded,  behind,  by  a  trans- 
verse groove  in  front  of  the  corpora  quadrigemina,  and  by  a 
slight  groove,   the   sulcus  habenulae,   externally.     That  de- 


50  THE    BRAIN    AND   SPINAL    CORD. 

pressed  surface  is  called  the  trigone  of  the  habenula.^^  Be 
neath  the  triangle  is  one  of  the  thalamic  nuclei.  The  outer 
area  is  seen  in  the  floor  of  the  lateral  ventricle.  It  presents 
an  anterior  elevation,  the  anterior  tubercle/^  beneath  which 
is  the  anterior  nucleus  of  the  thalamus.  A  sheet  of  epithe- 
lium, extending  from  the  fornix  to  the  taenia  semicircularis, 
covers  this  outer  area  and  separates  it  from  the  ventricular 
cavity. 

A  special  lamina  of  fibers,  the  external  medullary  lamina, 
derived  from  the  fillet,  forms  the  external  surface  of  the  optic 
thalamus  and  rests  upon  the  superior  lamina  of  the  internal 
capsule. 

The  inferior  surface  blends  with  the  superior  surface  of 
the  tegmentum  and  substantia  nigra,  and  forms  the  laminae 
and  nuclei  of  the  tegmental  region.     (See  below.) 

Hypothalamic  tegmental  regional  is  composeid  of  three 
layers:  (1)  Stratum  dorsale  next  the  optic  thalamus;  (2) 
Zona  incerta,  the  middle;  and  (3)  the  nucleus  of  Luys,  or 
hypothalamic  body,  the  inferior.  The  nucleus  of  Luys^^ 
is  but  the  terminal  part  of  the  substantia  nigra.  The  reticu- 
lar formation  of  the  tegmentum,  continuing  beneath  the  optic 
thalamus,  forms  the  zona  incerta.  The  stratum  dorsale  is 
made  up  as  follows:  (a)  Fibers  from  the  posterior  longi- 
tudinal bundle  (Meynert) ;  (b)  the  superior  peduncle  of 
cerebellum  (Forel),  in  which  is  the  upper  end  of  the  red 
nucleus^^  of  the  tegmentum;  and  (c)  the  fillet.^* 

The  external  geniculate  body  (geniculum,  a  little  knot  or 

(59)  Trig-onum   habenulse. 

(60)  Tuberculum   anterius  thalaml. 

(61)  Hypothalamus. 

(62)  Nucleus  hypothalamicus. 

(63)  Nucleus  ruber. 

(64)  Lemniscus. 


THE    CEREBRUM.  51 

knee)^'^'^  forms  a  slight  swelling  at  the  lowest  point  of  the 
optic  thalamus.  It  marks  the  apparent  end  of  the  outer  root 
of  the  optic  tract  and  is  the  terminal  nucleus  of  eighty  per 
cent.of  its  fibers.  It  is  joined  to  the  superior  quadrigeminal 
body -by  the  superior  brachium.  In  appearance  it  is  dark  col- 
ored and  laminated;  its  gray  matter,  which  contains  pig- 
mented multipolar  cell-bodies,  is  divided  into  thick  layers  by 
thin  laminae  of  fibers  from  the  optic  tract.  The  processes 
of  the  multipolar  cell-bodies  help  to  form  the  optic  radiations. 
The  internal  geniculate  body^<^  belongs  to  the  mid-brain. 
It  is  placed  at  the  end  of  the  inner  root,  as  the  external  genic- 
ulate is  at  the  end  of  the  outer  root,  of  the  optic  tract.  It 
rises  up  from  the  groove  between  the  optic  thalamus  and 
corpora  quadrigemina,  and  is  joineid  to  the  inferior  quadri- 
geminal body  by  the  inferior  brachium.  The  superior  bra- 
chium sweeps  around  it  in  front,  passing  between  it  and  the 
external  geniculate  body.  The  internal  geniculate  body  is 
gray  iii  color  and  is  not  laminated.  Its  cell-bodies  are  small, 
and  fusiform  in  shape.  They  perhaps  give  origin  to  the  in- 
tercerebral  fibers  (Gudden)  of  the  optic  tract  and  to  a  large 
number  of  the  acustic  radiations. 

(65)  Corpus   geniculatum   laterale. 

(66)  Corpus   geniculatum  mediale. 


CHAPTER  III. 


MID-BRAIN. 

The  brain  just  behind  the  cerebrum  is  the  mid-brain.^  It 
is  the  connecting  link  between  the  inter-brain  and  the  hemi- 
spheres, in  front,  and  the  pons,  behind.  This  has  suggested 
the  name  isthmus,  sometimes  applied  to  it,  though  isthmus  is 
more  specifically  applied  to  the  constriction  behind  the  cor- 
pora quadrigemina.  It  is  developed  from  the  middle  of  the 
five  brain  vesicles,  the  mesencephalon.  The  cerebral  hemi- 
spheres almost  conceal  it  from  view;  they  overhang  it  dor- 
sally,  and  the  temporal  lobes,  inclosing  it  between  them,  bend 
medially  and  cover  part  of  its  ventral  surface.  Only  the 
median  part  of  the  ventral  surface  is  visible  in  the  complete 
brain.  The  form  of  the  mid-brain  resembles  a  flattened 
cylinder.  Its  axis,  a  half  inch  long,  is  pointed  upward  and 
forward,  and  its  long  diameter,  which  varies  from  an  inch 
to  an  inch  and  a  quarter  in  length,  is  directed  transversely. 

SURFACES. 

The  mid-brain  has  four  surfaces,  viz.,  the  ventral  and 
dorsal,  which  are  free,  and  the  superior  and  inferior,  repre- 
senting the  ends  of  the  cylinder,  which  are  attached.  The 
two  latter  are  parallel  with  each  other  and  are  formed  by 
section. 

The  superior  surface,  sloping  downward  and  forward, 
meets  the  ventral  surface  at  an  acute  angle.  Its  inclination 
is  that  of  the  back  part  of  the  floor  of  the  third  ventricle. 

(1)    Isthmus  rhombencephali  and  mesencephalon. 


MID-BRAIN.  53 

External  to  the  floor  of  the  ventricle,  it  is  attached  to  the 
optic  thalami  anid  internal  capsules.  The  blending  of  it  with 
the  thalami  forms  the  structures  of  the  hypothalamic  teg- 
mental regions,  and  the  continuations  of  the  extreme  lateral 
portions,  the  crustse,  constitute  the  superior  laminae  of  the 
internal  capsules  of  the  hemispheres.  In  the  median  line  be- 
hind the  third  ventricle  it  is  attached  to  the  posterior  com- 
n^issure. 

The  inferior  surface  joins  the  upper  surface  of  the  pons. 
It  is  a  little  narrower  than  the  superior  surface.  It  is  about 
one  inch  broad  and  measures  three-quarters  of  an  inch  dor  so- 
ventrally. 

The  ventral  surface  of  the  mid-brain  looks  downward  and 
forward.  It  is  deeply  grooved  longitudinally  by  the  median 
stdcus,^  and  is  slightly  concave  from  above  downward.  It 
is  separated  on  either  side  from  the  dorsal  surface  by  the 
sulcus  lateralis.^  Though  partially  concealed  by  the  tem- 
poral lobes  of  the  cerebrum,  the  ventral  surface  is  unattached. 
It  is  formed  by  a  prominent  band,  the  crusta,'^  at  either  side; 
and  by  a  median  structure,  the  posterior  perforated  lamina,^ 
which  is  inclosed  between  the  two  crustae.  The  posterior  per- 
forated lamina  forms  the  floor  of  the  median  sulcus.  The 
inner  border  of  the  crusta  is  free  and  overhangs  the  per- 
forated lamina  slightly.  Thus  is  formed  the  oculomotor 
groove^  between  the  crusta  and  perforated  lamina,  whence 
the  third  cranial  nerve  takes  its  superficial  origin.  The 
fourth  nerve  courses  forward  over  the  ventral  surface,  but 
is  not  attached  to  it. 


(2)  Fossa  interpeduncularis. 

(3)  Sulcus  lateralis  mesencephali. 

(4)  Basis  pedunculi. 

(5)  Substantia  perforata  posterior. 

(6)  Sulcus  nervi  oculomotoril. 


54  THE    BRAIN    AND    SPINAL    CORD. 

The  dorsal  surface  of  the  mid-brain,  though  free,  is  en- 
tirely concealed  by  the  cerebral  hemispheres.  It  forms  part 
of  the  floor  of  the  great  transverse  fissure  and  is  covered  by 
pia  mater.  The  lateral  sulcus  bounds  it  on  each  side.  From 
the  sulcus  lateralis  it  elevates  abruptly  toward  the  median 
line,  where  it  presents  a  longitudinal  groove.  This  produces 
two  ridges  which  are  subdivided  by  a  transver-se  groove  into 
the  four  eminences  (colliculi)  of  the  corpora  quadngemina. 
On  either  side,  anterior  and  a  little  external  to  the  quadri- 
geminal  bodies,  is  the  internal  geniculate  body.  There  are 
thus  presented  six  eminences  on  the  dorsal  surface  of  the 
mid-brain.  The  entire  dorsal  surface  is  formed  by  the  teg- 
mentum. 

INTERIOR. 

The  mid-brain  is  made  up  of  three  great  divisions,  namely : 

(1)     The  ventral  part,  composed  of  the  two  crustae;  (2) 

the  substantia  nigra,  which  is  the  middle  part;  and  (3)  the 

dorsal  part,  called  the  tegmentum,  composed  of  lateral  halves 

united  by  a  raphe. 

The  crustae'^  are  two  rounded  bands  of  white  fibers,  limited 
by  the  medial  and  the  lateral  sulci,  which  form  the  ventral 
part  of  the  mid-brain.  They  are  in  contact  at  the  front  of 
the  pons,  from  which  they  diverge  upward  and  forward  and 
pierce  the  inferior  surface  of  the  cerebrum  beneath  the  optic 
tracts.  Entering  the  cerebrum  just  external  to  the  optic  thal- 
amus, the  fibers  of  each  crusta  spread  out,  fan-like,  in  the 
internal  capsule.  Excepting  the  medial  fillet,  a  part  of  which 
enters  the  inferior  lamina,  and  a  part  of  the  temporal  cerebro- 
corticopontal  tract  which  takes  the  same  course,  the  crusta 
enters  only  into  the  superior  lamina  of  that  inner  capsule. 

(7)    Basis   pedunculi    (sing-.). 


MID-BRAIN.  55 

The  deep  portion  of  each  crusta  is  occupied  by  the  interme- 
diate bundle,  whose  fibers  arise  in  the  corpus  striatum  and 
terminate  in  the  nucleus  pontis  (Flechsig).  The  superficial 
portion  should  be  studied  in  three  parts: 

(1)  The  outer  fifth  of  each  crusta,  the  temporal  cerebro- 
corticopontal  tract,  is  composed  of  efferent  fibers  which  rise 
in  the  temporal  cortex,  in  the  superior,  middle  and  inferior 
gyri  (Dejerine).  Proceeding  through  the  inferior  lamina 
and  the  occipital  segment  of  the  superior  lamina  of  the  inter- 
nal capsule,  and  through  the  lateral  part  of  the  crusta,  they 
terminate  chiefly  in  the  nucleus  of  the  pons;  a  few  end  in 
motor  nuclei  of  cranial  nerves  (Spitzka).  The  fibers  are 
probably  interrupted  in  the  thalamus  or  lenticular  nucleus. 
They  form  a  segment  of  the  indirect  motor  path.  These 
fibers  are  meduUated  later  than  the  pyramidal  tract  (Flech- 
sig). 

(2)  The  middle  three-fifths  ot  the  crusta  is  for  the  most 
part  motor.  It  is  called  the  pyramidal  tract.^  Its  fibers  rise 
in  the  Eolandic  area  of  the  cerebral  cortex;  they  form  the 
genu  and  anterior  two-thirds  of  the  posterior  segment  of  the 
internal  capsule,  the  middle  three-fifths  of  the  crusta,  the 
ventral  longitudinal  fibers  of  the  pons,  and  the  pyramid  of 
the  medulla.  Below  the  medulla  they  are  continued  in  the 
direct  and  crossed  pyramidal  tracts  of  the  spinal  cord.  Those 
fibers  of  the  pyramidal  tract  which  innervate  the  muscles  of 
speech  and  of  the  face  run  through  the  genu  of  the  internal 
capsule  and  constitute  the  medial  portion  of  the  tract.  Im- 
mediately behind  the  face  fibers,  in  the  capsula  interna,  and 
external  to  them,  in  the  tract,  are  fibers  which  innervate  the 
muscles  of  the  arm.  Still  behind  these,  in  the  internal  cap- 
sule, and  external  to  them,  in  the  pyramidal  tract  of  the 

(8)    Fasciculus   longitudinalis   pyramidalis. 


56  THE    BRAIN    AND    SPINAL    CORD. 

crusta,  are  fibers  for  the  innervation  of  the  trunk  and  leg 
mnscleSj  the  leg  fibers  being  most  posterior  and  most  external. 
Intermingled  with  the  pyramidal  fibers  are  a  few  fibers  from 
the  cerebellum.  The  cerebellar  fibers,  upon  reaching  the  pons 
through  the  middle  peduncle  of  the  cerebellum,  ascend  with 
tlie  ventral  longitudinal  fibers  of  the  pons  and  are  sparsely 
scattered  throughout  the  crusta. 

(3)  The  inne7'  fifth  of  the  crusta  is  composed  of  the  me- 
dial fillet  and  the  frontal  cerebro-corticopontal  tract.  The 
origin  of  the  latter  is  probably  in  the  pre-Eolandic  cortex,  at 
the  anterior  end  of  the  first  frontal  and  at  the  feet  of  the 
second  and  third  frontal  gyri ;  and,  perhaps,  in  the  middle  of 
the  gyrus  fornicatus.  It  is  motor.  This  motor  tract  is  con- 
tained in  the  anterior  segment  of  the  upper  lamina  of  the  in- 
ternal capsule.  Its  termination  is  in  the  nucleus  of  the  pons 
and  in  the  motor  nuclei  of  cranial  nerves  (Flechsig).  It  con- 
stitutes a  stage  of  an  indirect  motor  path,  like  the  fibers  of 
the  outer  fifth  of  the  crusta,  and  the  indirect  path  is  con- 
tinued to  the  opposite  half  of  the  cerebellum  by  neurones 
whose  cell-bodies  are  in  the  nucleus  pontis  (Flechsig).  The 
medial  fillet^  (sensory)  exists  as  a  distinct  bundle  in  this  part 
of  the  crusta.  Superiorly,  it  enters  the  hypothalamic  region, 
and  ends  in  the  ventre- lateral  nucleus  of  the  optic  thalamus. 
A  few  of  its  fibers  join  the  ansae  lenticularis  et  peduncularis 
and  run  uninterrupted  to  the  cortex ;  they  form  a  part  of  the 
inferior  lamina  of  the  internal  capsule,  and  then,  of  the 
medullary  laminae  of  the  lenticular  nucleus.  The  medial  fil- 
let is  the  afferent  cerebral  tract  of  the  spinal  and  of  all  the 
cranial  nerves  with  the  exception  of  the  cochlear  division  of 
the  auditory. 

The  Substantia  Nigra. — The  central  part  of  the  mid-brain 

(9)    Lemniscus   medialis. 


MID-BRAIN.  57 

is  a  sheet  of  pigmented  gray  matter.  The  substantia  nigra 
is  visible  at  the  base  of  the  brain  between  the  crustse,  where 
it  is  called  the  posterior  perforated  lamina,^^  and  its  margin 
comes  to  the  surface  in  each  lateral  sulcus.  Antero-pos- 
teriorly,  it  extends  from  the  pons  forward  to  the  corpora 
albican tia  and  nucleus  of  Luys.  Doisal  to  it  is  the  teg- 
mentum. Transversely,  the  substantia  nigra  is  convex  down- 
ward, but  it  is  slightly  concave  longitudinally.  The  third 
nerve  pierces  it  and  comes  out  through  the  oculomotor 
groove.  It  contains  small  pigmented  multipolar  cell-bodies, 
some  of  which  constitute  a  relay  for  certain  fibers  of  the 
medial  fillet  (Barker).  There  is  an  aggregation  of  these 
cells  located  medially  just  in  front  of  the  pons,  the  inter- 
peduncular ganglion}'^  According  to  Forel,  this  ganglion  is 
connected  by  a  bundle  of  fibers,  the  fasciculus  retroflexus, 
with  the  nucleus  habenulae  of  the  optic  thalamus.  The  an- 
tero-lateral  portion  of  the  substantia  nigra  forms  the  nucleus 
of  Luys,  or  nucleus  hypotlialamicus,  on  either  side.  The 
nucleus  Luysi  lies  ventro-lateral  to  the  red  nucleus,^  ^  ^nd  is 
separated  from  it  by  the  zona  incerta. 

The  Tegmentum. — The  dorsal  division  of  the  mid-brain, 
being  the  largest  and  covering  the  other  two  divisions,  is 
in  consequence  called  the  tegmentum  (the  cover).  It  fits 
ventrally  into  the  concavity  of  the  substantia  nigra,  and  is 
bounded  by  the  lateral  sulcus  on  each  side.  Dorsally,  it  pre- 
sents the  internal  geniculate  bodies  and  the  corpora  quadri- 
gemina.  The  tegmentum  is  very  thick  medially.  In  trans- 
verse section  it  has  a  pentagonal  form,  the  curve  of  the  sub- 
stantia nigra  representing  two  sides.  Superiorly,  the  an- 
terior extremity  of  the  tegmentum  blends  with  the  optic 

(10)    Substantia  perforata  posterior. 
(U)    Ganglion   interpedunculare. 
(12)    Nucleus  ruber. 


58  THE    BRAIN    AND    SPINAL    CORD. 

thalami  in  the  hypothalamic  regions.  The  tegmentum  is 
continuous  with  the  pons  behind  (caudalward).  It  contains 
the  cavity  of  the  mid-brain,  the  aqueductus  Sylvii.^^ 

The  Aqueduct  of  Sylvius. — ^The  aqueduct  is  a  very  slender 
canal  connecting  the  third  and  fourth  ventricles.  So  it  is 
the  "iter  a  tertia  ad  quartum  ventriculum."  It  is  situated 
near  the  dorsal  surface  of  the  tegmentum,  directly  beneath 
the  sulcus  longitudinalis.  It  is  a  half-inch  long.  In  shape  it 
is  V-like,  above;  elliptical,  in  the  middle,  with  a  vertical 
major  axis;  and  T-form,  below,  where  it  joins  the  fourth 
ventricle.  Its  height  varies  between  a  sixteenth  and  an  eighth 
of  an  inch.  Like  other  ventricles,  it  is  lined  with  ependyma. 
A  layer  of  gray  matter,  thickest  on  the  sides  and  floor,  sur- 
rounds the  aqueduct  of  Sylvius.  It  is  continuous  with  the 
gray  matter  of  the  fourth  ventricle.  In  it  are  the  nuclei  of 
the  oculomotor  (third)  and  the  trochlear  (fourth)  cranial 
nerves. 

Nuclei  of  the  Oculomotor  and  Trochlear  Nerves. — Both 
nuclei  extend  the  entire  length  of  the  aqueduct,  and  the 
oculomotor^*  is  prolonged  into  the  wall  of  the  third  ventricle, 
where  it  receives  a  bundle  of  fibers  from  the  opposite  pineal 
stria  and  optic  tract.  The  nuclei  are  composed  of  several 
elongated  masses  of  gray  matter,  which  contain  cell-bodies 
of  various  sizes.  They  lie.  side  by  side  in  each  half  of  the 
floor  of  the  aqueduct,  and  are  associated  with  the  optic  tract 
(external  root)  by  fibers  in  the  posterior  commissure  and  by 
association  neurones  in  the  superior  quadrigeminal  bodies. 
By  this  connection  certain  reflex  ocular  movement,  accommo- 
dation for  distance  and  pupillary  contraction  are  accom- 
plished. The  oculomotor  nucleus  is  next  the  median  line  and 
behind  unites  with  its  fellow  across  it.     For  the  most  part 

(13)    Aqueductus   cerebri.  (14)    Nucleus  oculomotorius. 


MID-BRAIN.  59 

the  third  nerve,  motor  oculi,  rises  from  the  nucleus  of  the 
same  side;  but  it  also  contains  crossed  fibers  from  the  oppo- 
site nucleus  and  from  the  posterior  longitudinal  bundle  of 
the  opposite  side.  Some  of  the  last  are  derived  from  the 
nucleus  of  the  abducent  (sixth)  nerve  and,  after  crossing  to 
the  third  nerve,  supply  the  internal  rectus  of  one  eyeball; 
while  the  sixth,  rising  from  the  same  nucleus,  supplies  the 
external  rectus  of  the  other  eye.  Thus  is  conjugate  deviation 
accounted  for.  The  third  nerve  passes  down  to  the  oculo- 
motor groove  through  tegmentum  and  substantia  nigra.  The 
root  fibers  of  the  fourth  nerve,  trochlear  (patheticus)^^  pro- 
ceed dorsally  and  caudalward  from  the  nucleus.  They  de- 
cussate with  the  fibers  from  the  opposite  nucleus  in  the  su- 
perior medullary  velum  (the  valve  of  Yieussens),  from  which 
they  emerge  on  either  side  of  the  frenulum.  They  then  con- 
tinue in  the  opposite  nerve  around  the  side  and  over  the 
ventral  surface  of  the  mid-brain.  The  nucleus  of  the  troch- 
lear nerve  (also  the  abducent)  likewise  receives  impulses 
from  the  optic  tract. 

The  corpora  quadrigemina  are  four  bodies  (colliculi) 
which  stand  upon  the  quadrigeminal  lamina  and  constitute 
a  large  part  of  the  dorsal  surface  of  the  mid-brain.  They  are 
seen  in  the  floor  of  the  great  transverse  fissure,  invested  by 
pia  mater  and  overhung,  anteriorly,  by  the  pineal  body.  The 
crucial  groove  separates  them  and  marks  out  a  larger  su- 
perior pair,^^  elongated  from  before  backward,  and  a  hemi- 
spherical inferior  pair.^"^  The  internal  geniculate  body  lies  in 
front  and  a  little  external  to  the  corpora  quadrigemina.  A 
ridge  made  up  of  white  fibers,  the  superior  brachium,^^  joins 

(15)  N.    trochlearis. 

(16)  Colliculi   superiores. 

(17)  Colliculi  inferiores. 

(18)  Brachium  quadrlgeminum  superius. 


60  THE    BRAIN   AND    SPINAL    CORD. 

each  superior  quadrigeminal  body  to  the  corresponding  exter- 
nal geniculate  body,  sweeping  around  the  internal  geniculate 
body  in  front  and  externally.  The  inferior  brachium^^  forms 
an  oblique  ridge  between  the  inferior  quadrigeminal  body  and 
the  corpus  geniculatum  internum  of  the  same  side.  The  su- 
perior peduncle  of  the  cerebellum  and  lateral  fiUet^o  form 
two  ridges  which  end  at  the  back  of  each  inferior  quadri- 
geminal body.  The  corpora  quadrigeniina  (superior  colli- 
culi)  constitute  the  great  center  for  the  association  of  ocular 
movements  and  reflexes  with  optic  and  auditory  impulses  and 
impulses  of  common  sensation.  The  inferior  colliculi  con- 
stitute a  relay,  or  way-station,  in  the  auditory  path. 

Structure. — The  corpora  are  composed  chiefly  of  gray  mat- 
ter. The  upper  and  lower  fillet  and  the  valve  of  Vieussens 
form  a  layer  of  fibers,  the  quadrigeminal  lamina,  upon  which 
they  rest  and  which  separates  them  from  the  gray  matter 
around  the  aqueduct  of  Sylvius.  They  also  contain  many 
fibers  in  their  interior  and  are  covered,  superficially,  by  a 
thin  layer  of  white  matter.  ( See  quadrigeminal  bodies, 
Chapter  IV.,  pages  82-83.) 

The  internal  geniculate  bodies^i  form  a  part  of  the  teg- 
mentum. They  are  derived  from  the  mesencephalon  with 
the  remainder  of  the  mid-brain  to  which  they  belong ;  but  for 
convenience,  they  were  considered  with  the  external  genicu- 
late bodies  under  the  heading  "inter-brain,"  which  see.  The 
internal  geniculate  bodies  form  the  relay  in  the  auditory  path 
next  above  the  inferior  quadrigeminal  bodies. 

Fibers  of  the  Tegmentum. — The  tegmentum  is  a  continua- 
tion of  the  dorsal  longitudinal  fibers  and  the  formatio  reticu- 

(19)  B.    quadrigeminum  inferius. 

(20)  Lemniscus  lateralis. 

(21)  Corpus  geniculatum   mediale   (sing.). 


MID-BRAIN.  OX 

laris  of  the  pons,  and  of  the  gray  matter  in  the  floor  of  the 
fourth  ventricle;  and,  in  addition,  has  the  geniculate  and 
quadrigeminal  ganglia  forming  its  dorsal  portion.  It  is 
composed  of  symmetrical  halves  united  by  a  median  raphe. 
Each  half  contains  innumerable  transverse  and  longitudinal 
fibers  with  small  masses  of  gray  matter  in  the  meshes.  In- 
tersecting the  many  transverse  fibers  are  six  distinct  bundles 
of  longitudinal  fibers.  They  descend  from  cerebrum  and 
mid-brain,  or  ascend  from  parts  below.  Those  six  bundles  are 
as  follows: 

(1)  The  Posterior  Longitudinal  Bundle^^  lies  beside  the 
raphe,  just  ventral  to  the  gray  matter  of  the  Sylvian  aque- 
duct. It  is  traceable  from  the  anterior  cornu  of  gray  mat- 
ter in  the  spinal  cord  where  its  ascending  fibers  rise  (Tscher- 
mak).  Being  chiefly  an  association  tract,  it  receives  fibers, 
in  the  pons,  from  the  cerebellum;  and  from  sensory  nuclei 
of  the  cranial  nerves,  in  the  medulla  and  pons.  It  carries 
motor  fibers  from  the  sixth  to  the  third  nerve;  also  descend- 
ing motor  fibers  from  the  nucleus  of  the  motor  oculi  to  the 
genu  of  the  seventh,  or  facial,  nerve.  These  latter  supply  the 
frontalis,  pyramidalis  nasi,  orbicularis  palpebrarum  and  cor- 
rugator  supercilii  muscles.  Through  the  raphe  the  posterior 
longitudinal  bundle  partially  decussates  with  its  fellow 
(lower  decussation).  These  fibers  pass  into  the  opposite 
third  and  fourth  and  other  motor  cranial  nuclei.  The  re- 
mainder of  the  bundle,  decussating  through  the  posterior 
commissure  (upper  decussation),  ends  in  the  pineal  body  and 
stratum  dorsale  of  the  hypothalamic  region.  It  connects  the 
cerebellum  with  opposite  nuclei  of  the  cranial  nerves  and 
the  latter  with  each  other.    It  associates  the  motor  oculi  with 

(22)    Fasciculus   longitudinalis   medialis. 


62  THE    BRAIN    AND    SPINAL    CORD. 

the  abducent  and  facial  nerves,  and  the  optic  with  the  ab- 
ducent.   It  also  associates  spinal  and  cranial  nerves. 

(2)  Anterior  Longitudinal  Bundle. — Just  ventral  to  the 
posterior  longitudinal  bundle  is  the  fasciculus  from  the  su- 
perior corpus  quadrigeminum  to  the  cilio-spinal  and  other 
centers  in  the  cord.     It  is  the  pupillo-dilator  tract. 

(3)  The  Fillet. — Near  the  upper  end  of  the  pons,  in  the 
ventral  part  of  the  formatio  reticularis,  the  fillet,  or  lemnis- 
cus, forms  a  very  broad  band  of  fibers  on  either  side  of  the 
median  raphe.  The  fillet  is  equal  in  width  to  half  the  trans- 
verse diameter  of  the  mid-brain.  It  continues  into  the  ven- 
tral portion  of  the  tegmentum,  but  immediately  divides  into 
two  fasciculi,  viz.,  the  interolivary  fillet,^^  and  the  lateral, 
or  lower,  fillet.^^  Farther  forward  a  small  bundle  leaves  the 
lateral  part  of  the  interolivar}^  fillet  and  runs  up  to  the  su- 
perior quadrigeminal  body.  That  bundle  is  called  the  su- 
perior fillet,25  and  what  remains  is  the  medial  fillet.^^ 

Function. — The  fillet  forms  a  segment  in  the  direct  sen- 
sory tract.  It  carries  spinal  and  cranial  impulses  to  the  cor- 
pora quadrigemina  and  optic  thalamus. 

Interolivary  Fillet. — The  fibers  composing  the  interolivary 
fillet  rise  chiefly  in  the  nucleus  gracilis  and  nucleus  cuneatus 
of  the  opposite  side  of  the  medulla  oblongata.  They  cross 
over  in  the  sensory  decussation  of  the  medulla ;  and,  excepting 
a  small  bundle,  terminate  in  the  ventro-lateral  nucleus  of  the 
optic  thalamus.  Fibers  are  added  from  masses  of  gray  mat- 
ter along  the  whole  course  of  the  interolivary  fillet,  especially 
from   the  terminal  nuclei  of  sensory    cranial    nerves;   and 


(23)  Lemniscus  interolivaris   (comprising  L.   medialis  and  L.   supe- 
rior). 

(24)  Lemniscus  lateralis. 

(25)  Lemniscus  superior. 

(26)  Lemniscus  medialis. 


MID-BRAIN.  63 

others,  also,  from  the  cerebellum.  On  the  other  hand,  cer- 
tain fibers  leave  the  fillet  and  end  in  the  nuclei  along  its 
course,  that  is,  are  interrupted,  and  other  fibers  continue  in 
their  stead.  A  small  bundle  of  fibers  separating  from  the 
lateral  part  of  the  interolivary  fillet  and  running  to  the  su- 
perior quadrigeminal  body,  forms  the  superior  fillet.  It  as- 
sociates ocular  movements  with  sensations  from  cranial  and 
spinal  nerves.  The  medial  fillet  bends  ventrally  as  it  runs 
through  the  mid-brain.  It  pierces  the  substantia  nigra,  in 
which  it  undergoes  a  partial  relay,  and  then  continues  for- 
ward, with  the  inner  fifth  of  the  crusta,  to  its  termination  in 
the  thalamus.  From  the  thalamus  the  impulses  are  carried 
by  the  anterior  stalk  and  ansae  lenticularis  et  peduncularis  to 
the  soma  esthetic  area  of  the  cortex. 

The  lateral,  or  lower,  fillet^'^  forms  an  oblique  ridge  on 
the  dorsum  of  the  tegmentum.  It  trends  upward  and  in- 
ward over  the  superior  cerebellar  peduncle  to  the  inferior 
quadrigeminal  body,  where  its  fibers  terminate.  It  rises 
chiefly  from  the  ventral  and  dorsal  parts  of  the  cochlear  nuclei 
(principally  the  opposite  one)  and  ends  in  the  inferior  quad- 
rigeminal body.  It  undergoes  partial  relay  in  the  nucleus 
of  the  superior  olive  and  of  the  trapezoid  body  on  each  side, 
and  the  nucleus  of  the  lateral  fillet  on  the  same  side,  and  it 
receives  a  small  bundle  of  fibers  from  the  anterolateral  as- 
cending, cerebellar  tract.  The  greater  number  of  its  fibers 
cross  through  the  trapezium;  some  are  uncrossed.  Thus  the 
lateral  fillet  forms  the  second  stage  in  the  auditory  conduc- 
tion path.  Tlie  auditory  nerve  constitutes  the  first  stage, 
the  lateral  fillet  the  second  stage,,  the  inferior  brachium  the 
third,  and  the  acustic  radiations  the  fourth  stage.    The  last 

(27)    Lemniscus  lateralis. 


64  THE    BRAIN   AND    SPINAL    CORD. 

stage  ends  in  the  cortex  of  the  superior  and  the  transverse 
temporal  convolutions. 

(4)  The  Superior  Pedunde^^  of  the  cerebellum  continues 
upward  from  the  dorsal  surface  of  the  pons.  It  forms  a  ridge 
near  the  median  line  of  the  mid-brain  which  ends  in  front 
at  the  inferior  corpus  quadrigeminum.  The  lower  fillet  winds 
inward  over  its  anterior  extremity.  It  is  joined  to  its  fellow 
by  a  sheet  of  white  matter,  the  valve  of  Vieussens.^^  The 
fibers  of  the  cerebellar  peduncles  bend  ventrally  beneath  the 
corpora  quadrigemina  and  then,  for  the  most  part,  decussate, 
inferior  to  the  iter,  through  the  median  raphe.  These  crossed 
fibers  with  the  few  uncrossed  run  forward  toward  the  in- 
ferior surface  of  the  optic  thalamus,  where  they  inclose  the 
red  nucleus,  and  help  to  form  the  stratum  dorsale  of  the  hy- 
pothalamic region  (Forel).  Many  of  the  fibers  terminate  in 
the  red  nucleus  and  from  it  others  rise  and  proceed  forward 
to  the  thalamus.  Though  most  of  the  superior  cerebellar  pe- 
duncle is  centripetal  and  forms  a  segment  of  an  indirect  sen- 
sory tract,  it  also  contains  effereiit  fibers  which  rise  in  the 
red  nucleus. 

(5)  The  Olivary  Fasciculus. — This  is  the  bundle^^  which 
takes  form  at  the  inferior  olive,  where  it  probably  rises.  It 
runs  through  the  formatio  reticularis  of  medulla  and  pons 
up  to  the  mid-brain.  In  the  tegmentum  it  pierces  the  de- 
cussation of  the  superior  cerebellar  peduncles,  running  ven- 
tral to  the  longitudinal  bundles;  and  then,  bending  lateral- 
ward,  it  ascends  external  to  the  posterior  longitudinal  bundle. 
It  ends  in  the  globus  pallidus  of  the  lenticular  nucleus 
(Flechsig).     Flechsig  believes  that  the  olivary  bundle  and 


(28)  Brachium   conjunctivum. 

(29)  Velum    modulare    anterius. 

(30)  Fasciculus   tegmenti   centralis. 


MID-BRAIN.  65 

the  fasciculus  triangularis  of  Helwig   (in  the  spinal  cord) 
are  parts  of  the  same  afferent  conduction  path. 

(6)  The  Crossed  Descending  Tract  of  the  Red  Nucleus. 
— Formed  by  axones  from  that  nucleus,  it  immediately  de- 
cussates with  its  fellow  of  the  opposite  side  and  descends,  in 
the  medial  part  of  the  lateral  fillet,  to  the  medulla;  it  then 
mingles  with  the  antero-lateral  ascending  cerebellar  tract,  in 
the  medulla;  and,  in  the  cord,  occupies  the  dorso-lateral  part 
of  the  crossed  pyramidal  tract.  It  ends  in  the  lateral  horn 
and  center  of  the  gray  crescent.  It  may  be  traced  to  the 
lumbar  segments  of  the  spinal  cord. 


CHAPTER  IV. 


THE  GRAY  AND  WHITE  MATTER  OF  THE  CERE- 
BRUM AND  MID-BRAIN. 

In  the  mid-brain,  white  matter  is  found  in  the  crustae 
and  tegmentum,  separated  by  the  gray  substantia  nigra;  and 
on  its  dorsum  are  the  corpora  quadrigemina  and  internal 
geniculate  bodies  composed  of  gray  matter.  Gray  matter 
forms  nearly  the  whole  of  the  inter-brain.  The  deep  part  of 
the  hemispheres  is  white  matter;  a  thin  envelope  of  gray 
matter,  the  cortex,  incloses  it.  Imbedded  in  that  white  mat- 
ter, is*  the  basal  ganglion  of  the  hemisphere,  called  the  corpus 
striatum.  Both  the  gray  and  the  white  matter  are  richly 
supplied  with  blood  vessels. 

The  Neurone. — The  essential  element  in  the  nervous  sys- 
tem is  the  neurone.  The  neurone  comprises  the  cell-body,  its 
processes  and  end-organs.  The  cell-body,  perikaryon,  or  nevr 
rone  center,  is  a  reticulated  mass  of  protoplasm  of  variable 
form,  and  ranges  between  ten  microns  and  fifty  microns  in 
size.  It  is  nucleated  and  may  possess  several  nucleoli.  Its 
shape,  which  is  spherical,  fusiform,  pyramidal,  stellate  or 
polygonal,  is  dependent  upon  the  number  and  mode  of  or- 
igin of  its  processes.  The  processes  of  the  neurone  are  from 
one  to  eight  or  a  dozen  in  number  and  are  of  two  kinds, 
namely,  the  dendrites  and  the  axones.  Dendrites,  like  the 
cell-body,  are  protoplasmic  in  composition  and  of  irregular 
contour,  except  in  sensory  nerves,  where  they  are  fibrillar, 
like  axones.     They  branch  richly  and  end  in  beaded  points. 


THE    GRAY   AND   WHITE    MATTER.  6/ 

They  conduct  toward  the  cell-body  and  are  therefore  affer- 
ent, or  sensory.  (N.  2,  Add.)  Axones,  or  neuraxones,  are 
smooth  and  fibrillar  in  character.  They  give  off  many  side 
branches,  called  collaterals,  and  terminate  by  multiple  di- 
vision in  an  end-hrush,  which  is  in  relation  with  another 
neurone  or  with  a  muscle  fiber.  In  the  latter  case  the  fibers 
of  the  end-brush  spread  out  into  disc-like  platelets,  motorial 
end-plates,  and  underneath  the  sarcolemmse  apply  themselves 
to  the  fibers  of  a  muscle.  Axones  conduct  from  the  neurone 
center.  They  are  efferent,  or  motor.  Both  axones  and  den- 
drites are  usually  insulated  by  the  white  substance  of 
Schwann,  which  forms  their  medullary  sheaths.  In  all  prob- 
ability neurones  differ  in  chemical  constitution  and  in  elec- 
tric status,  hence  chemicals,  electricity  and  diseases  appear 
to  exercise  a  selective  power  and  affect  certain  neurones  with- 
out influencing  others  (see  note  on  neurone,  p.  68). 

In  the  brain  and  spinal  cord  and  in  the  optic  nerves  two 
forms  of  sustentacular  tissue  are  found  supporting  the  neu- 
rones. (1)  Neuroglia,  which  is  most  abundant  in  gray  mat- 
ter. It  is  an  epiblastic  structure  made  up  of  richly  branched 
nucleated  cells  whose  processes  form  a  fine  reticulation  in 
the  larger  meshes  of  the  connective  tissue  network  (N.  3, 
Add.)  (2)  Connective  tissue  network. — That  is  of  mesoblaa- 
tic  origin  and  is  formed  by  branching  processes  from  the  in- 
ner surface  of  the  pia  mater.  It  transmits  the  blood-vessels 
into  the  nervous  substance.  The  neurones  constitute  53  per 
cent  of  the  brain  and  cord  (cell-bodies,  6  per  cent)  and  the 
sustentacular  tissue  47  per  cent  (Donaldson). 

The  white  matter  of  the  cerebro-spinal  axis  is  made  up 
chiefly  of  bundles  of  meduUated  axones  imbedded  in  neuroglia 
and  supported  by  connective  tissue.  The  fibers  possess  no 
neurolemma. 


68  THE    BRAIN   AND    SPINAL    CORD. 

The  gray  matter  of  the  central  nervous  system  is  composed 
of  cell-bodies  and  dendrites,  chiefly,  but  also  contains  axones. 
These  nerve  elements  are  supported  by  connective  tissue  and 
blood  vessels  and  are  imbedded  in  a  great  abundance  of  neu- 
roglia. The  nerve  fibers  in  the  gray  matter  are  to  a  large 
extent  non-meduUated. 


NOTE. 

In  the  first  edition  of  this  work  the  name  of  the  nerve  ele- 
ment was  spelled  "neuron"  according  to  Waldeyer.  But  the 
new  spelling,  already  used  by  Profs.  Barker  and  Gordinier 
in  their  excellent  works,  has  been  employed  in  the  revised 
edition  to  avoid  confusion.  Shaefer  uses  neuron  in  the  sense 
of  axone  and  Wilder  of  Cornell  makes  it  synonymous  with 
cerebro-spinal  axis. 

The  neurone  is  a  nervous  entity  and  in  the  embryo  is  struc- 
turally independent  of  all  other  neurones.  When  fully  de- 
veloped in  man  perhaps  a  very  small  number  of  neurones  are 
united  together  by  concrescence  or  protoplasmic  bridges,  but 
their  predominant  relation  is  certainly  that  of  contact,  or 
synapsis. 

TYPES  OF  NEURONES. 

1.  The  first  type  has  a  long  axone,  which  preserves  its 
identity  though  it  may  give  oS  many  collaterals.  Found  in 
brain  and  spinal  cord  (Deiter). 

2.  The  second  type  has  a  short  axone,  breaking  at  once 
into  branches  of  apparently  equal  importance,  the  dendrax- 
one.    Found  in  cerebrum  and  cerebellum  (Golgi^s  cells). 

3.  The  third  type  has  two  or  more  axones — diaxone,  tri- 
axone,  polyaxone — as  in  the  first  layer  of  the  cerebral  cortex 
(Cajal). 


THE    GRAY    AND    WHITE    MATTER.  69 

ORDERS  OF  NEURONES. 

1.  The  first  order  has  distal  process  in  relation  with  the 
periphery,  as  spinal-ganglion  or  anterior  comu  neurones. 

2.  The  second  order  has  cell-hody  or  distal  process  in  re- 
lation with  neurone  of  first  order.  In  like  manner  there  are 
neurones  of  the  third,  fourth,  fifth  order,  etc. 

FUNCTIONS    OF   NEURONES. 

1.    Afferent.    2.    Associative.    3.    Efferent. 

QUALITIES  PECULIAR  TO  DENDRITES  : 

1.  They  may  be  absent  or  very  numerous. 

2.  They  are  protoplasmic  in  composition  like  the  cell-body. 

3.  In  contour  they  are  irregular,  knobbed  or  gemmulated. 

Except  in  sensory  cranial  and  spinal  nerves  (Cajal). 

4.  End  in  sharp  points,  or  in  sensory  neurones  of  first  or- 

der, they  may  end  within  bulbous  or  spherical  end- 
organs. 

5.  Afferent  in  conduction:     (1)     sensory;  (2)     excito-re- 

flex;  and  (3)  trophic  (?). 

QUALITIES   PECULIAR   TO  AXONES I 

1.  Single  or  multiple  (absent  in  latent  neurones). 

2.  Fibrillar  in  character. 

3.  Smooth  and  regular  in  contour. 

4.  Terminate  in  form  of  end-tufts  which  in  motor  neurones 

of  the  first  order  form  motorial  end-plates. 

5.  Efferent  in  conduction:     (1)    motor;    (2)    inhibitory; 

(3)  trophic  (  ?)  ;  and  (4)  secretory  (  ?). 
On  section  both  dendrite  and  axone  undergo  Wallerian 
degeneration  in  the  disconnected  part.    That  part  remaining 
in  connection  with  the  cell-body  atrophies  and  degenerates 
late,  degeneration  of  Nissl. 


yO  THE    BRAIN    AND    SPINAL    CORD. 

The  gray  matter  of  the  cerebrum  and  mid-brain  is  con- 
veniently grouped  into  three  classes: 
I.     Cortical. 
II.     Ganglionar. 
III.     Central,  or  Ventricular. 

I.    The  Cortical  Gray  Matter. 

It  consists  of  a  thin  envelope,  the  cortex  (or  bark),  which 
forms  the  surface  of  the  hemispheres  and  incloses  the  (white) 
medulla,  the  centrum  semiovale.  The  cortex  varies  in  thick- 
ness from  a  line  to  a*  quarter  of  an  inch.  Thickest  on  the 
surface  of  the  convolution,  it  grows  thinner  to  the  bottom  of 
the  sulci.  It  is  of  a  reddish,  or  yellowish,  gray  color  depend- 
ing on  the  richness  of  the  blood  supply.  By  long  observation 
of  lesions  in  the  brain  and  by  anatomical  and  physiological 
investigation  the  cortex  has  been  mapped  out  into  quite  defi- 
nite areas.  Psychic  function,  probably,  is  dependent  upon  the 
associated  activity  of  all  parts  of  the  brain;  but  common 
sensory  and  motor  regions  have  been  defined  with  considera- 
ble exactness.  The  latter  are  found  in  the  equatorial  zone  of 
the  hemisphere  (Figure  1).  That  sensori-motor  region  is 
called  the  motor  area  (or  Ealandic  area)  when  referring  to 
the  efferent,  or  motor,  tracts  which  rise  in  it;  and,  when  ref- 
erence is  made  to  the  sensory  tracts  which  terminate  in  it,  the 
sensori-motor  region  is  called  the  somcesthetic  area.  Notice 
in  Fig.  1  that  the  motor  speech  center  and  head  area  comprise 
the  foot  of  the  inferior  frontal  convolution  and  the  lower  two- 
fourths  of  the  central  gyri;  the  writing  center  of  Gordinier 
and  the  upper  extremity  area  occupy  the  foot  of  the  middle 
frontal,  a  part  of  the  superior  frontal  and  the  third  fourth 
(numbered  upward)  of  the  central  convolutions;  and  the 
trunh  and  lower  extremity  areas  are  contained  in  the  upper 


THE    GRAY   AND    WHITE    MATTER.  7 1 

one-fourth  of  the  central  convolutions  and  in  the  superior  pa- 
rietal gyrus.  The  head,  shoulder,  trunk  and  lower  extremity 
are  also  represented,  and  in  this  order,  in  the  marginal  gyrus, 
the  paracentral  and  quadrate  lobules  (see  Fig.  2).  In  the 
same  figure  the  centers  of  smell  and  taste  may  be  observed  in 
the  uncus  and  hippocampal  convolution  and  the  visual  cen- 
ter in  the  cuneus.  The  latter  extends  somewhat  into  the  con- 
vex portion  of  the  occipital  lobe.  Locate  the  remaining  spe- 
cial centers  on  the  convex  surface  (see  Fig.  1).  In  the  angu- 
lar and  occipital  convolutions  is  the  center  for  visual  mem- 
ories; in  the  supramarginal  gyrus  appears  to  be  the  center 
for  motor  memories;  the  sensory  auditory  center  is  seen  in 
third  and  fourth  fifths  of  the  superior  and  in  the  transverse 
temporal  gyri,  and  the  center  of  auditory  memories  is  in  the 
immediately  adjacent  cortex.  The  naming  center  is  probably 
in  the  third  temporal  convolution. 

All  the  above  motor,  somgesthetic  and  special  sense  areas 
are  provided  with  projection  fibers  which  connect  them 
with  definite  muscle  groups  and  surface  regions  and  with 
the  organs  of  special  sense.  Other  parts  of  the  cerebral  cor- 
tex possess  no  projection  fibers;  they  are  believed  to  be  asso- 
ciative in  function.  Anterior  association  center. — According 
to  Flechsig,  that  part  of  the  frontal  cortex  which  is  anterior 
to  the  motor  and  somaesthetic  regions  determines  the  temper- 
ament and  individuality  of  the  person ;  while  the  posterior  as- 
sociation center,  composed  of  those  portions  of  cortex  situated 
between  the  sensory  and  motor  regions  of  the  equatorial  zone, 
in  front,  and  the  visual  cortex  of  the  occipital  lobe,  behind, 
determine  the  intelleetuality  of  the  individual.  To  acquire 
knowledge  of  the  external  world  is  thus  the  function  of  the 
posterior  association  center.     Flechsig  regards  the  island  of 


72  THE    BRAIN    AND    SPINAL    CORD. 

Eeil  as  the  middle  association  center  and  lesions  in  it  have 
been  found  associated  wfth  paraphasia. 

Destructive  lesions  of  parts  of  the  motor  or  sensory  cortex 
cause  merely  loss  of  certain  motions  and  sensations  repre- 
sented by  those  parts,  but  ablation  of  association  centers  dis- 
connects the  sensory,  the  memory  and  the  motor  regions  (as 
in  aphasia),  causes  change  of  temperament  and  impairment 
of  the  so-called  moral  and  intellectual  faculties.  Ablation 
of  the  visual  memory  center  or  auditory  memory  center  pro- 
duces mind-blindness  in  the  former  and  in  the  latter  mind- 
deafness. 

To  the  naked  eye  a  fresh  section  of  the  cerebral  cortex 
shows  a  stratified  arrangement;  sometimes  three  gray  lam- 
inae can  be  made  out  which  are  separated  by  the  inner  and 
outer  white  lines  of  Bailarger;  and,  in  the  hippocampus  ma- 
jor, a  superficial  (reticulated)  white  layer  also  is  easily  seen. 
A  typical  section  of  cortex,  which  is  usually  taken  from  the 
parietal  lobe,  presents  under  the  microscope  five  layers,  as 
follows  : 

(1)  The  Superficial,  Molecular,  or  Neurogliar  Layer.- — 
It  is  next  the  pia  mater  and  is  believed  to  be  associative  in 
function.     Neuroglia  forms  the  bulk  of  it,  but  it  contains 

(a)  a  few  irregular  cell-bodies  (Neurones  of  Cajal)  possess- 
ing dendritic  and  from  one  to  three  axonic  processes;  and 

(b)  a  fine  network  composed  of  gray  and  medullated  nerve 
fibers.  These  medullated  fibers  form  the  superficial  white 
layer,  above  referred  to,  visible  to  the  naked  eye  in  the  hip- 
pocampus major.  The  fibers  in  the  neurogliar  layer  are  for 
the  most  part  dendrites  of  cell-bodies  in  adjacent  laminae. 
The  neurones  of  the  first  layer  probably  give  rise  to  the  short 
association  fibers  of  the  cerebral  cortex.    (N.  4,  Add.) 

(2)  The  Second  Layer  is  the  layer  of  small  pyramids. 


THE    GRAY   AND    WHITE    MATTER.  73 

The  pyramids  are  closely  packed  together.  They  point  to- 
ward the  pia.  Their  dendrites  run  outward  and  ramify  in 
the  neurogliar  layer;  their  bases,  from  which  the  axones 
issue,  are  directed  toward  the  white  core  of  the  convolution. 
The  axones,  after  piercing  the  deeper  gray  laminae,  receive 
the  white  substance  of  Schwann  and  enter  into  the  forma- 
tion of  the  medulla  (the  centrum  semiovale)  of  the  hemi- 
sphere. The  small  pyramids  are  believed  to  be  chiefly  com- 
missural and  associative  in  function. 

(3)  Third,  the  Layer  of  Large  Pyramids. — The  large 
pyramids  have  the  same  direction  as  the  small  ones.  They 
are  arranged  in  elongated  groups  separated  by  radiating 
fibers.  The  pyramids  are  largest  in  the  Eolandic  area,  and 
the  grouping  is  most  distinct  near  the  underlying  fourth 
layer.  The  function  of  the  large  pyramids  is  chiefly  motor 
(Dana),  but  it  is  also  commissural  and  associative  (Cajal). 
Their  dendritic  processes  pass  outward;  their  axones,  as  me- 
duUated  fibers,  run  down  into  the  white  center  and  capsula 
interna.  Seven  or  eight  collaterals  are  given  off  from  each 
axis-cylinder  process  before  it  becomes  meduUated,  and  these 
collaterals  ramify  in  the  adjacent  gray  matter,  basal  ganglia, 
etc. 

The  third  layer  is  as  thick  as  the  two  overlying  it;  it 
varies  between  one-fiftieth  and  one-twenty-fifth  of  an  inch. 
Its  formation  is  like  that  of  the  cornu  Ammonis,  the  hippo- 
campus major. 

(4)  Fourth,  the  poiyviorphons  layer,  is  a  very  thin  one, 
about  a  hundredth  of  an  inch  in  thickness.  Its  cell-bodies 
are  small  and  irregular.  They  possess  many  dendrites  and 
one  axone,  or  axis-cylinder  process.  A  few  of  the  latter,  pierc- 
ing the  third  and  second  layers  of  gray  substance,  ramify  in 
the  first;  the  larger  number  of  them  proceed  into  the  white 


74  THE    BRAIN    AND    SPINAL    CORD. 

center  and  comprise  a  great  number  of  the  commissural  and 
long  association  fibers  (Cajal).  Probably  others  become  ef- 
ferent projection  fibers.     (Note  5,  Add.) 

(5)  Fifth. — This  is  the  layer  of  fusiform  cell-bodies.  It 
has  the  formation  of  the  claustrum,  hence  the  synonym 
for  the  fifth  layer,  the  claustral  formation.  It  is  placed 
next  the  white  center.  It  is  a  thick  layer,  one-twenty-fifth  of 
an  inch,  and  merges  imperceptibly  into  the  medulla  beneath 
it.  The  cell-bodies  in  the  main  have  their  long  axes  perpen- 
dicular to  the  surface  of  the  hemisphere;  but,  beneath  the 
fissures,  they  are  parallel  with  it.  In  the  convolutions  they 
lie  between  the  radiating  fibers.  Under  the  sulci  they  are 
parallel  with  the  association  fibers  which  join  adjacent  gyri. 
The  commissural  and  long  association  fibers  belong  for  the 
most  part  to  the  fusiform  and  polymorphous  neurones.  (N. 
5  and  6,  Add.) 

To  this  typical  cortex  there  are  four  principal  exceptions, 
viz. : 

(a)  On  the  medial  surface  of  the  occipital  lobe,  near  the 
cdlcarine  fissure,  there  are  six  to  eight  layers  produced  by 
the  division  of  the  layer  of  large  pyramids  by  a  lamina  of 
irregular  cell-bodies,  with  or  without  the  presence  of  the 
normal  fourth  layer.  The  latter  may  divide  the  fifth  layer. 
There  are  very  few  large  pyramids  in  this  situation. 

(b)  The  gray  cap  of  the  olfactory  hulh  has  but  four 
layers,  namely:  first,  the  nerve  fiber  layer  composed  of  the 
non-medullated  fibers  of  the  olfactory  nerves  which  join  the 
bulb  from  below;  second,  the  stratum  glomerulosum,  the 
glomeruli  being  made  up  of  the  synapses  formed  by  the  ol- 
factory fibers  and  the  dendrites  of  the  mitral  neurones; 
third,  the  layer  of  mitral  cell-bodies,  whose  protoplasmic  pro- 
cesses ramify  in  the  second  layer  and  whose  axones  pass  into 


THE    GRAY    AND    WHITE    MATTER.  75 

the  medullary  stem,  after  piercing  the  granular  layer;  and, 
fourth,  the  granular  layer,  which  lies  next  the  medullary 
stem  and  is  composed  of  small  irregular  neurone-centers,  like 
those  in  the  rust-colored  granular  layer  of  the  cerebellum. 
The  last  two  (the  third  and  fourth)  are  sometimes  called 
the  granular  layer,  thus  reducing  the  number  to  three.  The 
axis-cylinder  processes  of  the  mitral  (or  conical)  neurones, 
medullated,  form  the  olfactory  tract. 

Destruction  of  the  olfactory  bulb,  olfactory  tract  or  olfac- 
tory area  in  the  cortex  causes  almost  exactly  the  same  re- 
sult, viz.,  anosmia  in  the  same  side  of  the  nose.  The  ol- 
factory path  is,-  chiefly,  if  not  entirely,  uncrossed. 

(c)  In  the  Jiippocampus  major  are  five  layers  of  cortical 
matter,  which  represent  the  first  four  of  typical  cortex.  The 
first  layer,  the  one  bounding  the  dentate  fissure,  is  the  invo- 
luted medullary  lamina.  This  is  the  regular  network  of 
medullated  fibers,  but  is  more  highly  developed  than  in  typi- 
cal cortex.  It  is  just  beneath  the  pia,  a  little  neuroglia  only 
intervening.  The  second  layer  is  composed  of  closely  packed 
small  cell-bodies  (granules).  It  is  the  stratum  granulosum. 
There  are  no  neurone-centers  in  the  third  layer,  but  a  dense 
network  of  pyramid  and  granule  dendrites.  The  first  three 
layers  represent  the  neurogliar  layer  of  typical  cortex.  The 
fourth  is  a  very  thick  layer  and  is  made  up  of  pyramids  of 
medium  size.  To  the  fourth  layer  the  second  and  third  lay- 
ers in  typical  cortex  correspond.  The  medullated  axones  of 
the  pyramids  constitute  the  thin  lamina  of  white  matter 
called  the  alveus  which  forms  the  ventricular  surface  of  the 
hippocampus  major.  Fifth. — ^Between  the  alveus  and  the 
pyramids  is  a  thin  polymorphous  layer,  which  resembles  the 
fourth  layer  of  parietal  cortex. 

(d)  The  fourth  exception  to  the  typical  cortex  is  found  in 


76  THE    BRAIN   AND    SPINAL    CORD. 

the  floor  of  the  fissure  of  Sylvius.  It  consists  of  a  very  great 
thickening  of  the  fusiform  layer.  All  five  laminae  are  pres- 
ent.   This  cortex  resembles  the  claustrum. 

The  claustrum  (a  rampart)  is  an  isolated  sheet  of  gray 
matter,  in  structure  much  like  the  fifth  layer  of  the  cortex. 
It  is  cortical  matter,  according  to  Meynert.  It  is  a  vertical 
antero-posterior  sheet  placed  medial  to  the  island  of  Eeil, 
and  lateral  to  the  external  capsule.  The  surface  in  contact 
with  the  external  capsule  is  smooth,  but  the  external  surface 
is  convoluted  to  coincide  with  the  gyri  insulse.  At  its  lower 
border  it  Joins  the  lenticular  nucleus.  It  is  made  up  of  fusi- 
form cell-bodies,  which  lie  between  the  fibers  of  the  uncinate 
fasciculus  (see  below — association  fibers). 

II.     Ganglionar  Gray  Matter. 

w  It  is  found  in  the  great  ganglia  which  have  already  been 

considered.  They  should  be  re-studied  in  this  connection. 
They  are  as  follows : 

1.  In  the  hemisphere: 

Corpus  striatum,  composed  of  the  caudate  and  the 
lenticular  nucleus. 

2.  In  the  inter-brain : 

The  optic  thalamus,  the  external  geniculate  body, 
nucleus  Luysi  and  red  nucleus. 

3.  In  the  mid-brain: 

The  internal  geniculate  body,  the  anterior  and  the 
posterior  quadrigeminal  body,  a  lateral  half  of  the 
substantia  nigra,  and  other  less  important  nuclei 
in  the  tegmentum. 
The  corpus  striatum  is  an  ovoid  mass  of  reddish-gray  mat- 
ter containing  pigmented  multipolar  cell-bodies  of  various 
sizes,  those  of  large  size  being  more  numerous  in  the  nucleus 


THE  GRAY  AND  WHITE  MATTER.  ']'] 

lenticularis  than  in  the  nucleus  ccmdcdus.  The  axones  of 
those  cell-bodies  run  both  toward  the  pons  and  toward  the 
cerebral  cortex.  The  corpus  striatum,  therefore,  forms  a 
way-station  in  an  efferent  conduction  tract  and,  perhaps  a 
less  important  one,  in  an  afferent  tract. 

Of  the  Centrifugal  Fibers  note  the  following  three  bundles : 
(a)  A  large  bundle  of  axones  from  the  striate  body,  the 
intermediate  tract,  runs  down  through  the  internal  capsule 
and  crusta  to  the  nucleus  pontis.  It  forms  a  thin  inter- 
mediate zone  between  the  pyramidal  tract  and  substantia 
nigra  in  the  mid-brain.  Axones  from  the  nucleus  pontis 
continue  the  tract  to  the  cerebellum  (Flechsig).  (b)  Eding- 
er's  bundle  rises  in  the  caudate  nucleus  and  in  the  putamen 
of  the  lenticular  nucleus  and,  running  through  the  anterior 
segment  of  the  internal  capsule,  terminates  in  the  optic 
thalamus,  chiefly;  but  also  in  the  substantia  nigra  and 
inferior  quadrigeminal  body,  (c)  The  centrifugal  axones 
of  the  ansa  lenticularis.  They  rise  principally  from  the  puta- 
men of  the  lenticular  nucleus.  After  running  through  the 
medullary  lamina  of  that  nucleus  they  proceed  medialward 
beneath  the  globus  pallidus.  The  greater  number  end  in  the 
nucleus  of  Luys;  certain  others  terminate  in  the  optic  thal- 
amus and  the  remainder  in  the  tuber  cinereum  and  gray  mat- 
ter in  the  lateral  wall  of  the  third  ventricle. 

The  best  known  Centripetal  Fibers  received  by  the  corpus 
striatum  are  (a)  certain  fibers  of  the  medial  fillet  contained 
in  the  ansa  lenticularis,  and  (b)  the  olivary  bundle  (Flech- 
sig). They  arborize  about  the  cell-bodies  in  the  globus 
pallidus,  whence  other  axones  rise  and  continue  to  the  somaes- 
thetic  area  of  the  cerebral  cortex. 

Lesions  of  the  corpus  striatum  affect  the  internal  capsule 
and  may  cause,  if  extensive,  hemiplegia  and  hemianesthesia 


78  THE    BRAIN   AND   SPINAL    CORD. 

of  the  opposite  side  of  the  body  and  partial  deafness  chiefly 
in  the  opposite  ear  and  hemianopia  of  the  corresponding 
halves  of  both  retinae. 

The  optic  thalanms^  is  made  up  chiefly  of  gray  matter 
containing  multipolar  and  fusiform  cell-bodies.  The  white 
matter,  the  internal  medullary  lamina,  divides  the  gray  into 
nuclei,  of  which  Nissl  has  described  about  twenty.  They 
may  be  grouped  as  follows: 

(1)  The  internal,  or  medial,  nucleus  is  joined  to  the 
opposite  inner  nucleus  by  the  gray  (or  middle)  commissure 
and  is  continuous  with  the  gray  matter  in  the  wall  and  floor 
of  the  third  ventricle;  but  the  internal  medullary  lamina 
separates  it  from  the  other  nuclei  of  the  same  thalamus. 

(3)  The  external,  or  lateral,  nucleus  is  the  largest.  It 
extends  from  dorsal  to  ventral  surface  the  entire  length  of 
the  thalamus  (Burdach).  It  forms  the  terminal  nucleus  for 
the  larger  part  of  the  tegmental  fibers  and  the  nucleus  of 
origin  for  most  of  the  fibers  of  the  ansae  peduncularis  et 
lenticularis  and  anterior  stalk  of  the  thalamus.  Destruction 
of  this  nucleus  interrupts  the  common  sensory  path,  and 
causes  hemianesthesia  of  the  opposite  side. 

(3)  The  nucleus  of  the  anterior  tubercle,  or  anterior 
nucleus,  receives  the  anterior  pillar  of  the  fornix  through 
the  bundle  of  Vicq  d^Azyr. 

(4)  The  posterior  nucleus  is  a  small  one.  It  is  situated 
under  the  pulvinar  between  the  geniculate  bodies. 

(5)  The  nucleus  of  the  pulvinar  is  an  important  one.  It 
receives  about  twenty  per  cent  of  the  optic  fibers  and  gives 
rise  to  a  corresponding  number  of  the  afferent  fibers  in  the 
optic  radiations  to  the  occipital  lobe,  hence  a  lesion  of  the 
pulvinar  impairs  vision. 

(1)    Thalamus. 


THE    GRAY    AND    WHITE    MATTER.  79 

(6)  The  nucleus  of  the  habenula  belongs  to  the  epithala- 
mus.  It  lies  beneath  the  trigonum  habenulse.  It  receives 
fibers  from  the  rhinencephalon  through  the  pineal  stria,  also 
fibers  from  the  optic  tract,  and  originates  a  bundle  of  fibers, 
fasciculus  retroflexus  (Meynert),  which  may  be  traced  back 
through  the  tegmentum  to  the  interpeduncular  ganglion  in 
the  substantia  nigra. 

(7)  The  central  nucleus  (center  median  of  Luys)  is 
situated  deep  in  the  thalamus  below  and  between  the  internal 
and  external  nuclei  and  dorsal  to  the  red  nucleus.  It  gives 
origin  to  some  fibers  of  the  ansa  lenticularis  which  run  to  the 
cortex.  \.  ■ .  v-     . 

The  white  matter  of  the  optic  thalamus  has,  for  the  most 
part,  an  indefinite  arrangement.  Into  it  enter  the  tegmental 
and  fillet  fibers  and  end,  chiefly,  in  the  lateral  nucleus.  It 
also  receives  axones  or  collaterals  from  every  part  of  the 
cerebral  cortex  and  sends  fibers  to  the  somaesthetic  and  spe- 
cial sense  areas.  The  white  matter  forms  the  S-shaped  in- 
ternal medullary  lamina  and  is  continued  in  numerous 
bundles  of  fibers  which  enter  the  hemisphere.  These  bundles 
are  as  follows: 

(1)  The  anterior  pillar  of  the  fornix,  having  pierced  the 
thalamus,  descends  to  the  corpus  albicans,  while  the  bundle 
of  Vicq  d'Azyr,2  which  rises  there,  ascends  to  the  thalamus 
and  terminates  in  its  anterior  nucleus. 

(2)  From  the  external  surface  two  groups,  which  rise 
chiefly  in  the  lateral  nucleus,  proceed  into  the  cortex  of  the 
general  sensory  region  (the  somaesthetic  area)  :  (a)  The  in- 
ferior is  the  ansa  peduncularis.  It  passes  below  the  lenticular 
nucleus  with  the  internal  capsule,  and  enters  into  both  the 
medullary  laminae  of  that  nucleus  and  the  external  capsule. 

(2)    Fasciculus   mamlllaris. 


80  THE    BRAIN    AND   SPINAL    CORD. 

It  ends  chiefly  in  the  cortex  of  the  ascending  frontal  and 
ascending  parietal  convolutions.  Its  fibers  are  medullated  at 
the  beginning  of  the  ninth  month  (Flechsig).  (b)  The 
superior  group  is  the  ansa  lenticularis,  which  pierces  the 
superior  lamina  of  the  internal  capsule  and  then  the  nucleus 
lenticularis,  where  some  of  its  fibers  are  interrupted.  It 
assists  in  forming  the  external  capsule  and  ends  in  the  cen- 
tral gyri,  the  paracentral  lobule,  the  foot  of  the  superior 
frontal  convolution  and  the  entire  limbic  lobe.  The  fibers 
of  the  ansa  lenticularis  become  medullated  at  the  end  of  the 
ninth  month  (Flechsig). 

(3)  The  anterior  stalk  streams  from  the  anterior  end  of 
the  lateral  nucleus,  via  the  frontal  segment  of  the  internal 
capsule,  into  the  frontal  lobe.  The  fibers  of  the  stalk  end  in 
the  cortex  at  the  foot  of  the  inferior  and  middle  frontal  gyri, 
the  anterior  half  of  the  superior  frontal  convolution  and  the 
middle  of  the  gyrus  fornicatus.  Its  fibers  receive  their 
medullary  sheaths  near  the  end  of  the  tenth  month 
(Flechsig).  From  the  same  part  of  the  cerebral  cortex  the 
frontal  cerebro-corticopontal  tract  rises. 

The  ansae  peduncularis  et  lenticularis  and  the  anterior 
stalk  of  the  thalamus  are  called  the  cortical  fillet;  they  carry 
ordinary  sensations,  chiefly  from  the  fillet  and  superior  cere- 
bellar peduncles,  up  to  the  somaesthetic  cortex.  Interruption 
of  the  cortical  fillet  stops  all  common  sensory  impulses. 

(4)  A  large  pencil  of  fibers,  the  optic  radiations,^  passes 
from  the  pulvinar  and  external  geniculate  body  through 
internal  capsule  to  the  visual  centers  in  the  occipital  lobe.  A 
number  of  the  optic  radiations  are  efferent  and  end  in  the 
superior  quadrigeminal  body.  Destructive  lesion  of  the  optic 
radiations  of  either  side  produces  hemianopia  of  the  same  side 
of  both  retinae. 

(3)    Radiatio   occipitothalamica. 


THE    GRAY    AND    WHITE    MATTER.  8 1 

(5)  Another  pencil  of  fibers  radiates  from  the  region  of 
the  internal  geniculate  body  through  internal  capsule  to  the 
jiuditory  area  in  the  temporal  lobe.  It  constitutes  the  acustic 
radiations^  If  the  acustic  radiations  be  destroyed  the  result 
is  partial  deafness  affecting  chiefly  the  opposite  ear. 

The  red  nucleus^  of  the  tegmentum  is  situated  beneath 
the  optic  thalamus.  It  is  a  way-station  in  the  indirect  sen- 
sory tract,  receiving  the  opposite  superior  cerebellar  peduncle 
and,  by  its  axones,  continuing  the  tract  to  the  optic  thalamus 
and  somaesthetic  cortex.  It  also  receives  efferent  axones  and 
gives  origin  to  two  bundles:  (a)  One  centrifugal  bundle  of 
axones  (the  crossed  descending  tract),  after  crossing  over  in 
the  tegmentum,  descends,  first,  with  the  medial  portion  of 
the  lateral  fillet;  second,  through  the  lateral  area  of  the 
medulla,  and,  third,  through  the  dorso-lateral  part  of  the 
crossed  pyramidal  tract  in  the  spinal  cord.  Gradually  di- 
minishing, it  disappears  at  the  first  lumbar  segment.  It  ends 
in  the  lateral  horn  and  center  of  the  gray  crescent  of  the 
spinal  cord,  (b)  The  red  nucleus  also  sends  a  bundle  of 
axones  through  the  opposite  superior  peduncle  of  the  cere- 
bellum to  the  corpus  dentatum. 

The  nucleus  hypothalamicus  (Luysi)  is  a  pigmented  bi- 
convex mass  of  gray  matter  placed  ventro-lateral  to  the  red 
nucleus,  and  between  it  and  the  fibers  of  the  crusta.  It 
constitutes  an  important  relay  for  certain  fibers  of  the  medial 
fillet.  Certain  descending  fibers  from  the  striate  body  termi- 
nate in  this  nucleus.  It  is  also  Joined  to  the  lamina  cinerea 
and  tuber  cinereum  by  a  bundle  of  fibers  that  accompanies 
Gudden's  commissure  along  the  medial  part  of  the  optic  tract. 
This  bundle  constitutes  Meynert's  commissure. 


(4)  Radiatio  temporothalamlca. 

(5)  Nucleus  ruber. 


82  THE    BRAIN    AND   SPINAL    CORD. 

The  external  geniculate  lody,^  which  receives  eighty  per 
cent  of  the  optic  fibers  (Von  Monokow)  and  forms  a  relay 
in  the  optic  path,  and  the  internal  geniculate  hody,'^  which 
is  a  way-station  in  the  auditory  tract,  have  been  sufficiently 
described.  Ablation  of  the  former  interrupts  the  optic  path, 
and  of  the  latter  the  auditory  path. 

The  superior  pair  of  the  corpora  quadrigemina^  represent 
the  corpora  bigemina,  the  optic  lobes,  of  birds,  fishes  and 
reptiles.  They  are  composed  of  three  laminae:  (1)  The 
superficial  white  matter,  the  stratum  zondle.  That  layer 
with  the  fibers  of  the  interior  is  continuous,  through  the 
superior  brachium,  with  the  optic  tract  and  radiations.  Many 
of  them  are  crossed  fibers.  (2)  The  stratum  cinereum  forms 
a  cap  of  gray  matter  beneath  the  stratum  zonale.  In  struc- 
ture it  resembles  the  gray  substance  of  the  inferior  bodies. 
(3)  Its  multipolar  cell-bodies  increase  in  size  toward  the 
second  gray  layer,  the  stratum  opticum.  In  that,  the  cell- 
bodies  are  very  large.  They  are  grouped  in  masses  between 
the  abundant  fibers  from  the  outer  root  of  the  optic  tract, 
which  arborize  about  them.  They  give  rise  to  axones  which 
associate  the  optic  fibers  with  the  nuclei  of  the  third,  fourth 
and  sixth  cranial  nerves,  and  with  the  cilio-spinal  center  in 
the  cervical  cord.  The  stratum  opticum  rests  upon  the  quad- 
rigeminal  lamina.  Some  gray  matter  is  scattered  through 
the  latter,  and  Tartuferi  calls  it  the  "stratum  lemnisci/'  The 
superior  quadrigeminal  body  forms  a  terminal  nucleus  for 
certain  fibers  of  the  superior  lemniscus,  which  bring  to  it 
ordinary  sensations  from  spinal  and  cranial  nerves. 

A  bundle  of  fibers  (the  anterior  longitudinal  bundle)  rises 
from  the  superior  quadrigeminal  body,  and  descends  along 

(6)  Corpus  geniculatum  lateraJe. 

(7)  Corpus  geniculatum   mediale. 

(8)  Colliculi    anteriores    corporum    quadrigeminorum. 


THE    GRAY    AND    WHITE    MATTER.  83 

the  ventral  surface  of  the  opposite  posterior  longitudinal 
bundle  to  the  anterior  cornu  of  gray  matter  in  the  spinal 
cord.  This  bundle  rises  in  relation  with  the  optic  fibers  and 
ends  in  the  cilio-spinal  center,  which  gives  origin  to  white 
rami  communicantes,  and  in  other  motor  centers.  It  forms 
one  segment  of  a  reflex  arc  concerned  in  dilating  the  pupil. 

Destructive  lesions  affecting  the  superior  quadrigeminal 
bodies  produce  loss  of  reflex  movement  of  the  eyeballs,  loss 
of  pupillary  reflex  and  loss  of  accommodation. 

In  the  inferior  pair  of  the  quadrigeminal  bodies^  the  white 
fibers  are  continuous,  behind,  with  the  lateral  fillet ;  and  with 
the  inferior  brachium,  antero-externally.  The  deep  part  of 
the  inferior  bodies  is  gray  matter.  It  contains  a  network  of 
fine  fibers,  and  small  multipolar  cell-bodies.'  The  latter  are 
in  relation  with  the  terminal  end-tufts  of  the  lateral  (lower) 
fillet  fibers,  and  give  origin  to  the  fibers  of  the  inferior  brach- 
ium. The  inferior  bodies  are  united  beneath  the  sulcus  longi- 
tudinalis  both  by  decussating  fibers  of  the  fillet  and  by  gray 
matter.  In  distinction  from  the  superior  bodies,  the  inferior 
pair  may  be  called  the.  auditory  lobes ;  they  are  well  marked 
only  in  those  mammals  having  highly  specialized  organs  of 
hearing,  and  form  an  important  way-station  in  the  auditory 
conduction  path,  hence  their  destruction  causes  the  same 
symptoms  as  interruption  of  the  acustic  radiations,  namely, 
deafness  affecting  chiefly  the  opposite  ear. 

Substantia  Nigra. — The  small  pigmented  multipolar  cell- 
bodies  which  make  up  the  substantia  nigra  form,  first,  a 
terminal  nucleus  for  certain  fibers  of  the  medial  fillet  and  a 
nucleus  of  origin  for  other  fibers  which  continue  in  that 
tract  (Barker)  ;  and,  second,  a  terminal  way-station  for  the 
fasciculus  retroflexus  of  Meynert  and  for  certain  flbers  of 

(9)    Colliculi  posteriores  corporum  quadrigeminorum. 


84  THE    BRAIN    AND    SPINAL    CORD. 

Edinger^s  bundle  from  the  corpus  striatum  (see  pages  77, 
79).  Beyond  this  terminal  station  the  efferent  tracts  are 
probably  continued,  but  they  have  not  been  traced. 

III.     Central,  or  Ventricular,  Gray  Matter. 

It  is  located  (1)  in  the  floor  and  walls  of  the  third  ven- 
tricle, (2)  in  the  middle  commissure  of  that  ventricle,  and 
(3)  around  the  Sylvian  aqueduct. 

(1)  The  lamina  cinerea  and  tuber  cinereum  form  a  sheet 
of  gray  substance  that  connects  the  inferior  surfaces  of  the 
hemispheres  and  may  be  called  their  inferior  (or  great)  gray 
commissure.  From  the  floor  of  the  third  ventricle  it  extends 
laterally  beneath  the  optic  thalamus,  and  is  continuous  with 
the  anterior  perforated  lamina.  The  gray  matter  of  the  floor 
extends  up  a  short  distance  on  the  medial  surface  of  the 
thalamus  opticus;  and  in  that  upturned  part  is  located  the 
anterior  end  of  the  motor  oculi  nucleus.  The  inferior  gray 
commissure  receives  efferent  fibers  through  the  ansa  lenticu- 
laris  from  the  corpus  striatum,  and  is  joined  to  the  nucleus 
of  Luys  by  the  fibers  of  Meynert's  commissure. 

(2)  The  middle  commissures^  joins  the  internal  nuclei  of 
the  optic  thalami.  It  is  continuous  with  this  upward  exten- 
sion of  the  gray  floor  of  the  third  ventricle.  In  the  middle 
commissure  are  cell-bodies  and  transverse  fibers.  The  latter 
appear  to  be  loops  which  reach  only  to  the  median  line;  at 
least  many  of  the  fibers  do  not  cross  to  the  opposite  side. 

(3)  The  nuclei  of  the  oculomotor  (third)  and  of  the 
trochlear  (fourth)  cranial  nerves  are  found  in  the  gray  mat- 
ter about  the  Sylvian  aqueduct.  In  it  also  is  a  part  of  the 
motor  nucleus  of  the  trigeminal,  or  fifth,  nerve.  Lesions 
which  involve  the  trochlear  and  oculomotor  nuclei,  as  a  rule, 

(10)    Massa  intermedia. 


THE  GRAY  AND  WHITE  MATTER.  85 

also  involve  the  fibers  of  the  tegmentum,  and  the  result  is 
ocular  paralysis  on  the  same  side  and  impaired  sensation 
(hemiataxia)   on  the  opposite  side  of  the  body. 

The  white  matter  of  the  cerebrum  and  mid-brain  is  com- 
posed of  three  definite  systems  of  fibers: 

1.  Projection,  or  peduncular,  fibers. 

2.  Transverse,  or  commissural,  fibers. 

3.  Association  fibers. 

I.     Projection  Fibers. 

They  are  composed,  first,  of  the  medullated  axis-cylinders 
of  the  large  and  medium-sized  pyramids  and  of  a  few  of  the 
polymorphous  neurones  in  the  cerebral  cortex;  and,  second, 
of  medullated  axones  of  neurones  whose  centers  are  situated 
in  masses  of  gray  matter  below  the  cerebral  cortex.  The 
projection  fibers  are  therefore  both  centrifugal  and  centripe- 
tal. They  run  through  the  mid-brain  to  the  cerebral  cortex 
and  vice  versa,  connecting  the  cortex,  directly  or  indirectly, 
with  all  parts  of  the  body,  throwing  or  projecting  a  picture 
of  every  part  and  organ  upon  the  cerebral  cortex.  Many  of 
the  fibers  are  interrupted  in  the  basal  ganglia,  especially  of 
ihe  centripetal  fibers.  Within  the  hemisphere  the  projection 
fibers  help  to  form  the  centrum  semiovale  and  the  corona 
radiata  and  then,  converging,  form  the  internal  capsule. 
More  distally,  in  the  mid-brain,  they  are  divided  into  two 
great  groups  of  fibers,  the  crusta  and  the  tegmentum,  sepa- 
rated by  the  substantia  nigra. 

CENTRIFUGAL,  OR  MOTOR,  PROJECTION  FIBERS. 

The  Crustae  comprise  most  of  the  centrifugal,  or  motor, 
fibers,  namely,  the  intermediate  bundle,  the  frontal  cerebro- 
corticopontal  tract,^^  the  p3rramidal  tract  and  the  temporal 

(11)    Tractus   cerebro-corticopontalis  frontalis. 


86  THE    BRAIN   AND    SPINAL    CORD. 

cerebro-corticopontal  tract.^^  The  intermediate  tract  extends 
from  the  corpus  striatum  through  the  deep  part  of  the  crusta 
to  the  motor  cranial  nuclei  and  to  the  nucleus  pontis,  whose 
axones  run  by  way  of  the  middle  cerebellar  peduncle  to  the 
cortex  of  the  opposite  hemisphere  of  the  cerebellum.  It  thus 
forms  a  segment  of  an  indirect  (through  the  cerebellum) 
efferent,  or  motor,  path.  The  fronto-pontal  tract^^  rises  from 
the  feet  of  the  second  and  third  frontal  gyri  and  the  anterior 
half  of  the  first  frontal  gyrus  and  from  the  middle  of  the 
gyrus  fomicatus.  It  traverses  the  centrum  semiovale,  corona 
radiata,  anterior  segment  of  the  internal  capsule  and  internal 
one-fifth  of  the  crusta  to  the  ventral  area  of  the  pons,  where 
it  terminates  in  the  nucleus  pontis  (chiefly)  and  in  the  nuclei 
of  motor  cranial  nerves  (Flechsig).  According  to  Dejerine, 
the  temporo-pontal  tract^^  extends  from  the  temporal  lobe 
through  the  inferior  lamina  (and  posterior  part  of  the 
superior  lamina)  of  the  internal  capsule  and  outer  one-fifth 
of  the  crusta  to  the  same  nucleus;  but  according  to  Spitzka 
some  of  its  fibers  end  in  nuclei  of  motor  cranial  nerves.  Thus 
it  should  be  noted  that,  with  the  exception  of  those  fibers  to 
motor  nuclei  of  the  cranial  nerves,  each  of  the  three  tracts 
above  mentioned — viz.,  the  intermediate,  fronto-pontal  and 
temporo-pontal — constitutes  a  segment  of  an  indirect  efferent 
path  which  is  interrupted  in  the  nucleus  pontis  and  then  con- 
tinued by  the  axones  of  that  nucleus  through  the  middle 
peduncle  of  the  cerebellum. 

Axones  from  the  Eolandic  cortex  constitute  the  Pyramidal 
Tract.13  Descending  through  the  centrum  semiovale,  corona 
radiata,  genu  and  anterior  two-thirds  of  the  posterior  segment 
of  the  internal  capsule,  the  pyramidal  tract  comprises  the 

(11)  Tractus  cerebro-corticopontalls  frontalis. 

(12)  T.   cerebro-corticopontalis  temporalis. 

(13)  Fasciculus   longitudinalis    (pyramidalis)   pontis. 


THE    GRAY    AND    WHITE    MATTER.  8/ 

middle  three-fifths  of  the  crusta,  the  ventral  longitudinal 
fibers  of  the  pons,  the  pyramid  of  the  medulla  and  the  crossed 
and  uncrossed  pyramidal  tracts  of  the  spinal  cord.  The 
fibers  of  the  pyramidal  tract,  with  a  few  exceptions,  cross 
over  to  the  opposite  side;  they  end  in  the  motor  nuclei  of 
cranial  and  spinal  nerves.  Fibers  enter  the  nucleus  of  the 
trochlear  (or  fourth  cranial)  nerve  on  the  same  side  and  a 
few  descend  to  the  motor  nuclei  of  other  cranial  nerves  and 
to  the  anterior  cornu  of  gray  matter  in  the  spinal  cord  with- 
out decussation;  all  other  pyramidal  fibers  terminate  on  the 
side  opposite  to  their  origin.  Cranial  fibers. — Those  fibers  of 
the  pyramidal  tract  which  end  in  the  nuclei  of  cranial  nerves 
rise  in  the  lower  (two-fourths)  and  anterior  part  of  the 
Eolandic,  or  motor,  area,  including  also  that  part  of  the 
marginal  convolution  situated  above  the  genu  of  the  corpus 
callosum.  They  run  through,  the  genu  of  the  internal  cap- 
sule and,  chiefly,  through  the  inner  portion  of  the  middle 
three-fifths  of  the  crusta ;  a  considerable  number  run  through 
the  outer  portion  of  the  pyramidal  area.  They  terminate  in 
the  motor  nuclei  of  cranial  nerves.  Upper  extremity  fibers. — 
The  fibers  of  the  pyramidal  tract  that  end  in  the  cervical  part 
of  the  spinal  cord,  and  through  it  innervate  the  muscles  of 
the  upper  extremity,  take  their  origin  from  that  part  of  the 
central  convolutions  (third  fourth)  adjacent  to  the  foot  of 
the  middle  frontal  gyrus,  the  foot  of  the  superior  frontal 
gyrus  and  the  adjoining  part  of  the  marginal  gyrus  next 
behind  the  head  center  and  directly  above  the  anterior  part 
of  the  truncus  corporis  callosi.  These  fibers  run  through  the 
posterior  segment  of  the  internal  capsule  just  behind  the 
genu,  and  through  the  crusta  immediately  external  to  the 
cranial  fibers.  Those  fibers  which  innervate  the  muscles  of 
the  thumb,  fingers  and  hand,  rise  lowest  down  in  the  arm 


88  THE    BRAIN    AND   SPINAL    CORD. 

area  of  the  cortex  and  occupy  the  posterior  part  of  the  arm 
bundle  in  the  internal  capsule  and  the  external  part  of  it  in 
the  crusta.  The  fibers  which  control  the  shoulder  muscles 
rise  in  the  upper  part  of  the  cortical  area  and  form  the 
anterior  and  internal  part  of  the  arm  bundle  in  the  capsula 
interna  and  crusta,  respectively,  while  the  wrist,  fore-arm, 
elbow  and  arm  are  innervated  by  means  of  fibers  which  are 
intermediate  in  both  origin  and  course.  Trunk  fibers. — The 
trunk  fibers  of  the  pyramidal  tract  rise  in  the  superior  fourth 
of  the  ascending  frontal  gyrus  and  in  the  contiguous  part  of 
the  marginal  convolution  immediately  in  front  of  the  para- 
central lobule.  In  the  internal  capsule  the  trunk  fibers  run 
just  behind  those  to  the  fingers  and  just  external  to  them  in 
the  crusta.  Lower  extremity  fibers. — A  large  number  of  the 
pyramidal  fibers  terminate  in  the  lumbar  enlargement  of 
the  spinal  cord  and  carry  impulses  to  the  nerves  of  the  lower 
extremity.  They  originate  in  the  upper  fourth  of  the  as- 
cending parietal  convolution,  in  the  superior  parietal  gyrus 
and  in  the  paracentral  and  quadrate  lobules.  The  hip  fibers 
rise  farthest  forward  and  the  toe  fibers  farthest  iDackward, 
immediately  in  front  of  the  parieto-occipital  fissure.  The 
fibers  have  the  same  relative  position  in  the  internal  capsule ; 
in  the  crusta  the  hip  fibers  are  internal  and  the  toe  fibers 
external.  Fibers  which  innervate  the  muscles  of  the  thigh, 
leg  and  small  toes  have  this  same  relative  position  and  order 
between  the  hip  and  great  toe  fibers  both  in  their  cortical 
origin  and  in  their  course  through  the  internal  capsule  and 
crusta. 

Several  bundles  of  centrifugal  fibers  are  found  in  the  teg- 
mentum, namely,  the  anterior  longitudinal  bundle,  the  crossed 
descending  tract  of  the  red  nucleus,  a  small  part  of  the  supe- 
rior peduncle  of  the  cerebellum,  the  descending  root  of  the 


THE    GRAY   AND   WHITE    MATTER.  89 

trifacial  nerve  and  certain  fibers  in  the  formatio  reticularis. 
With  these  exceptions  the  tegmentum  is  centripetal,  or  sen- 
sory. 

Destruction  by  clot,  tumor,  or  otherwise,  of  any  of  the 
above  motor  tracts  causes  (upper  segment)  paralysis  of  the 
particular  muscles  innervated  through  that  tract. 

CENTRIPETAL,   OR   SENSORY,    PROJECTION   FIBERS. 

The  sensory  fibers  of  the  tegmentum  comprise  the  olivary 
bundle,  the  fillets,  the  optic  tract  (outer  root),  and  the 
greater  part  of  the  posterior  longitudinal  bundle  and  superior 
cerebellar  peduncle;  perhaps,  also,  certain  fibers  in  the  for- 
matio reticularis.  Excepting  a  small  number  of  fibers,  all 
these  bundles  terminate  in  the  basal  ganglia;  but  the  paths 
of  conduction  are  continued  through  the  internal  capsule. 
In  the  capsula  interna  the  centripetal  projection  fibers  con- 
stitute the  three  systems  of  Flechsig  (the  cortical  fillet)  and 
the  optic  and  aeustic  (and  gustatory?)  radiations.  The 
former  end  in  the  somgesthetic  area  of  the  cerebral  cortex, 
the  latter  in  the  visual,  auditory  and  gustatory  cortex. 

The  exact  origin  of  the  Three  Systems  of  Flechsig  has  not 
been  determined,  but  they  are  known  to  rise,  chiefly,  in  the 
lateral  nucleus  of  the  optic  thalamus.  The  ansa  peduncularis 
(first  system  of  Flechsig)  runs  through  the  internal  capsule 
behind  the  pyramidal  tract  in  the  inferior  lamina.  Some  of 
its  fibers  enter  the  medullary  laminae  of  the  nucleus  lenticu- 
laris  and  others  enter  the  external  capsule;  ultimately  they 
all  terminate  in  the  central  convolutions.  The  ansa  lenticu- 
laris  (second  system  of  Flechsig)  issues  from  the  lateral 
surface  of  the  thalamus  higher  up  than  the  former  loop  and 
mingles  with  the  pyramidal  fibers  in  the  internal  capsule.  A 
number  of  its  fibers  pierce  the  internal  capsule    (superior 


QO  THE    BRAIN    AND   SPINAL    CORD. 

lamina)  and  are  interrupted  in  the  lenticular  nucleus;  they 
assist  in  forming  the  medullary  laminae  of  that  nucleus  and 
form  a  part  of  the  external  capsule.  The  lenticular  loop 
terminates  in  the  upper  part  of  the  central  convolutions,  the 
foot  of  the  superior  frontal  gyrus,  the  paracentral  lobule  and 
the  entire  limbic  lobe.  From  the  anterior  end  of  the  optic 
thalamus  streams  a  great  pencil  of  fibers,  called  the  anterior 
stalk  (third  system  of  Flechsig).  It  mingles  to  a  small  ex- 
tent with  the  fibers  of  the  pyramidal  tract,  but  runs  chiefly 
through  the  anterior  segment  of  the  internal  capsule.  The 
anterior  stalk  terminates  in  the  feet  of  the  inferior  and 
middle  frontal  convolutions,  in  the  anterior  half  of  the  su- 
perior frontal  gyrus  and  in  the  middle  of  the  gyrus  f ornicatus. 
The  three  systems  of  Flechsig  convey  common  sensory  im- 
pulses to  the  somsesthetic  area  of  the  cerebral  cortex.  They 
are  often  called  the  cortical  fillet. 

If  the  cortical  fillet  be  severed,  all  common  sensory  im- 
pulses to  that  hemisphere  are  interrupted  and  complete  loss 
of  sensation  on  the  opposite  side  of  the  body  (hemiataxia) 
results. 

The  Acustic  Radiations  and  the  Inferior  Brachium  con- 
tinue the  auditory  path  from  the  end  of  the  lateral  fillet,  in 
the  inferior  quadrigeminal  body,  to  the  internal  geniculate 
body  and  then,  through  the  retrolenticular  part  of  the  internal 
capsule,  to  the  transverse  temporal  gyri  and  the  third  and 
fourth  fifths  of  the  superior  temporal  convolution  (Barker). 
Interruption  of  these  fibers  produces  deafness  in  the  opposite 
ear,  which  is  not  complete  because  the  acustic  path  is  not 
wholly  crossed. 

The  Optic  Radiations  rise  in  the  external  geniculate  body 
and  in  the  pulvinar  of  the  optic  thalamus.  They  continue 
the  visual  conduction  path  through  the  retrolenticular  region 


THE    GRAY    AND    WHITE    MATTER.  QI 

of  the  internal  capsule  to  the  cortex  of  the  cuneate  lobe. 
Half-blindness  in  the  same  side  of  both  retinae  results  from 
section  of  the  optic  radiations. 

II.  Commissural  Fibers. 

They  connect  opposite  sides  of  the  cerebrum.  They  are 
contained  chiefly  in  the  corpus  callosum,  the  anterior  commis- 
sure, and  the  commissura  hippocampi  (N.  7,  Add.). 

The  Corpus  Callosum  is  the  great  link  between  the  hemi- 
spheres. Its  fibers  connect  both  similar  and  dissimilar  parts 
of  the  cortices.  It  is  made  up  of  cortical  axones,  a  few  of 
them  being  projection  fibers;  and  collaterals  from  the  asso- 
ciation and  projection  fibers.  All  callosal  fibers,  except  the 
few  peduncular  fibers,  end  on  the  opposite  side  in  arboriza- 
tions within  the  cortex. 

The  Anterior  Commissure  joins  the  opposite  temporal  and 
occipital  lobes  together  (pars  occipito-temp oralis)  ;  and  the 
limbic  lobes  with  each  other  and  with  the  contra-lateral 
olfactory  tract  (pars  olfactoria). 

The  Commissura  Hippocampi,  the  lyre,  unites  the  hippo- 
campus major,  the  uncus  and  the  optic  thalamus  with  their 
fellows  of  the  opposite  side. 

III.  Association  Fibers. 

These  fibers  remain  on  the  same  side  and  connect  parts  of 
the  same  hemisphere.  They  are  situated  within  or  close  to 
the  cortex,  the  various  parts  of  which  they  serve  to  unite. 
The  Short  Association  Fibers  are  probably  the  axones  of  the 
irregular  cell-bodies  (Cajal's)  situated  in  the  neurogliar 
layer  of  the  cortex.  They  unite  contiguous  parts  of  the  same 
convolution  and  associate  together  adjacent  convolutions. 
They  comprise  arcuate  and  tangential  fibers.  They  are  the 
more  numerous  and  very  important.    Among  them  are  fibers 


92  THE    BRAIN    AND    SPINAL    CORD. 

which  connect  the  visual  sensory  area  with  the  visual  mem- 
ory area  and  the  auditory  sensory  with  the  auditory  memory 
area.  Interruption  of  these  association  fibers  gives  rise  to 
certain  forms  of  sensory  aphasia  (N.  4,  Add.). 

The  Long  Association  Fibers  are  collected  into  bundles. 
The  long  association  fibers  rise  chiefly  from  the  polymorph- 
ous and  fusiform  layers  of  the  cerebral  cortex,  but  also,  to 
some  extent,  from  the  pyramids  in  the  second  and  third  layers 
(Cajal).  They  are  axones.  Proceeding  out  of  the  lobe  in 
which  they  rise,  they  arborize  about  neurones  in  more  or  less 
distant  parts  of  the  cortex.  The  long  association  fibers  dip 
down  into  the  centrum  semiovale  and  bring  into  harmonious 
action  the  widely  separated  cerebral  centers.  Among  the 
best  known  are  the  following  bundles: 

(1)  The  Cingulum,  or  the  fillet  of  the  gyrus  fornicatus, 
is  a  bundle  of  fibers  in  the  falciform  gyrus  (the  fornicate  and 
hippocampal  gyri),  which  almost  entirely  encircles  the  cor- 
pus callosum.  It  extends  from  the  anterior  perforated 
lamina,  through  the  gyrus  fornicatus  and  hippocampal  con- 
volution, to  the  uncus.  The  fibers  have  been  divided  into 
three  groups  by  Beevor,  namely:  (a)  The  anterior,  which 
joins  the  anterior  perforated  lamina  and  internal  olfactory 
root  to  the  fore  part  of  the  frontal  lobe,  (b)  The  horizontal, 
which  unites  the  frontal  lobe  and  the  gyrus  fornicatus.  And 
(c)  the  posterior  fasciculus,  which  associates  the  lingual  and 
fusiform  gyri  with  the  hippocampal  gyrus  and  pole  of  the 
temporal  lobe. 

(2)  The  Fornix. — Each  lateral  half  of  the  fornix^*  is  a 
bundle  of  association  fibers.  Its  anterior  end  (or  pillar)  is 
connected  with  the  corpus  albicans;  and,  through  the  bundle 
of  Vicq  d'Azyr,  also  with  the  optic  thalamus.    The  posterior 

(14)    Corpus  fornicis. 


THE    GRAY   AND   WHITE     MATTER.  93 

pillar,  descending  in  the  middle  horn  of  the  lateral  ventricle, 
for  the  most  part,  disappears  in  the  hippocampus  major  (its 
origin)  ;  but  a  small  bundle  of  its  fibers,  constituting  the 
corpus  fimbriatum,  continues  to  the  uncus. 

(3)  The  Uncinate  Fasciculus  is  a  bundle,^^  with  some 
sharply  curved  fibers,  which  arches  over  the  main  stem  of  the 
Sylvian  fissure,  and  connects  the  uncus  and  the  orbital  part 
of  the  frontal  lobe.  It  is  situated  near  the  basal  surface.  Its 
fibers  spread  out  at  both  ends  in  the  cortex,  and  they  espe- 
cially join  the  internal  and  posterior  orbital  and  the  third 
frontal  convolution  with  the  limbic  lobe  (Barker).  Like  the 
cingulum  and  fornix,  it  is  connected  with  the  rhinencephalon. 
Lesion  in  any  one  of  these  three  bundles  causes  disturbance  of 
smell. 

(4)  The  Superior  Longitudinal  Fasciculus'^^  is  a  sagittal 
bundle  located  beneath  the  convex  surface  of  the  hemisphere, 
just  above  the  horizontal  ramus  of  the  fissure  of  Sylvius.  It 
joins  the  frontal  cortex  with  the  parietal  and  the  external 
temporal.  It  thus  associates  the  auditory  and  the  visual  mem- 
ory centers  with  the  motor  speech  center;  hence,  aphasia  is 
the  result  of  its  interruption. 

(5)  The  Inferior  Longitudinal  Fasciculus'^'^  is  about  on  a 
level  with  the  lateral  ventricle.  It  passes  near  the  outer  wall 
of  the  descending  and  posterior  cornua  of  that  ventricle,  and 
connects  the  temporal  lobe  to  the  occipital.  In  the  temporal 
lobe  its  fibers  cross  at  right  angles  those  of  the  inferior  lamina 
of  the  internal  capsule.  This  fasciculus  unites  the  auditory 
and  visual  memory  centers,  and  thus  associates  the  memories 
of  things  seen  with  the  memories  of  things  heard. 

(6)  The  Fasciculus  Occipito-frontalis  (Forel). — This  is 

(15)  Fasciculus  uncinatus. 

(16)  Fasciculus  longitudinalis  superior, 

(17)  Fasciculus  longitudinalis  inferior. 


94  THE    BRAIN    AND    SPINAL    CORD. 

a  large  bundle  of  fibers  formerly  regarded  as  a  part  of  the 
corpus  eallosum.  It  is  situated  between  the  cingulum  and 
the  superior  longitudinal  bundle.  Just  external  to  the  lateral 
ventricle.  It  extends  from  the  cortex  of  every  part  of  the 
frontal  lobe  to  the  cortex  of  the  convex  surface  and  lateral 
border  of  the  occipital  lobe.  Posteriorly,  the  fibers  diverge 
to  form  a  fan-like  sheet,  and  that  sheet  enters  into  the  ex- 
ternal boundary  of  the  descending  horn  of  the  lateral  ventricle 
and  into  the  fioor,  lateral  wall  and  roof  of  the  posterior  horn, 
hence  the  synonym,  tapetum.  Its  particular  function  is  un- 
known. 

(7)  The  Perpendicular  Fasciculus}^ — This  is  a  very 
broad  vertical  bundle  located  just  in  front  of  the  occipital 
lobe.  Anteriorly,  it  extends  from  the  inferior  parietal  con- 
volution, above,  down  to  the  second  and  third  temporal ;  and, 
posteriorly,  it  joins  the  superior  occipital  convolution  with  the 
middle  and  inferior  occipital  and  with  the  fusiform  gyrus  of 
the  temporal  lobe.    Its  function  is  doubtful. 

NOTE. 

The  student  will  find  many  obscure  points  cleared  up  by 
a  careful  study  of  the  embryology  of  the  cerebrum  (see 
Chap.  XI.,  page  202). 

BLOOD   SUPPLY   OP   THE    CEREBRUM   AND   MID-BRAIN. 

The  blood  supply  of  the  cerebrum  and  mid-brain  is  de- 
rived from  the  anterior  choroid  and  the  anterior  and  middle 
cerebral  arteries,  all  branches  of  the  internal  carotid;  and 
from  the  posterior  cerebral  arteries,  which  are  terminal 
branches  of  the  basilar  artery.  They  form  a  remarkable 
anastamosis  at  the  base  of  the  brain,  the  circle  of  Willis.^  ^ 
The  Circle  of  Willis    (really  a  heptagon)   extends  from  a 

(18)    Fasciculus  perpendicularis.        (19)    Cireulus   arteriosus. 


THE    GRAY   AND    WHITE     MATTER.  95 

point  in  the  great  longitudinal  fissure,  anterior  to  the  optic 
commissure,  back  to  the  pons.  It  is  about  an  inch  and  a 
half  long,  and  one  inch  in  transverse  diameter.  In  front  are 
the  anterior  cerebral  arteries  converging  forward  from  the 
internal  carotids  and  uniting  through  the  anterior  communi- 
cating artery.2<^  The  posterior  communicating  artery^^  forms 
the  lateral  boundary  of  the  circle.  It  forms  the  anastamosis 
between  the  internal  carotid  artery  and  the  posterior  cere- 
bral. The  posterior  cerebral  arteries  bound  the  circle  be- 
hind. The  superior  cerebellar  arteries  send  several  branches 
to  the  dorsum  of  the  mid-brain. 

The  large  distal  'branches  of  the  cerebral  arteries  are  dis- 
tributed chiefly  to  the  cortex  and  medulla  of  the  hemispheres ; 
while  the  small  proximal  hranches  supply  the  ganglia  and 
inter-brain.  The  former  belong  to  the  cortical  system,  the 
latter  to  the  ganglionic  system. 

CORTICAL   SYSTEM. 

The  Anterior  Cerebral  Artery22  enters  the  great  lon- 
gitudinal fissure.  Winding  aronnd  the  genu  of  the  corpus 
callosum,  it  runs  back  on  the  medial  surface  of  the  hemi- 
sphere to  the  parieto-occipital  fissure.  It  has  three  branches : 
(1)  Anterior  internal  frontal,  which  supplies  the  internal 
orbital  convolution  and  olfactory  bulb,  the  superior  frontal 
and  the  anterior  half  of  the  middle  frontal  gyri.  (2)  Mid- 
dle internal  frontal,  which  is  distributed  to  the  corpus  cal- 
losum, gyrus  fornicatus,  marginal  convolution  and  upper 
end  of  the  ascending  frontal  convolution.  And  (3)  Posterior 
internal  frontal,  which  supplies  the  quadrate  lobe  and  part 
of  the  superior  parietal  convolution. 

The  Middle  Cerebral  Artery23  runs  in  the  fissure  of 
Sylvius.    It  has  four  distal  branches :    (1)  External  and  infe- 

(20)  A,    communicans   anterior.         (22)    Artera  cerebri  anterior. 

(21)  A.  communicans  posterior.        (23)    Artera  cerebri  media. 


g6  THE    BRAIN   AND   SPINAL    CORD. 

rior  frontal,  to  the  anterior  and  posterior  orbital  and  third 
frontal  convolutions;  (2)  Ascending  frontal,  and  (3)  As- 
cending parietal,  to  convolutions  of  the  same  name.  The 
ascending  frontal  also  supplies  the  foot  of  the  middle  frontal 
gyrus;  and  the  ascending  parietal  artery,  a  part  of  both  the 
superior  and  inferior  parietal  convolutions.  And  (4)  Parieto- 
temporal, which  supplies  the  supragmarginal  and  the  angular 
and  the  superior  and  middle  temporal  gyri. 

The  Posterior  Cerebral  Artery,^*  winding  from  the  basilar 
artery25  outward  around  the  mid-brain,  breaks  up  into  three 
cortical  branches  on  the  tentorial  surface  of  the  hemisphere. 
Their  distribution  is  as  follows :  ( 1 )  Occipital,  to  the  cuneus 
and  the  convex  surface  of  the  occipital  lobe;  (3)  Uncinate, 
to  the  same  convolution  (hippocampal  and  lingual),  and  (3) 
Temporal  (or  temporo-sphenoidal),  to  the  fourth,  third  and 
part  of  the  second  temporal  gyri. 

These  vessels  of  the  cortical  system  and  their  many 
branches  pierce  the  hemispheres  perpendicular  to  the  surface. 
They  are  distributed,  the  short,  to  the  cortex,  and  the  long, 
to  the  medulla  of  the  hemispheres.  To  a  limited  extent  they 
anastamose  with  one  another,  but  they  do  not  communicate 
with  the  ganglionic  system. 

GANGLIONIC    SYSTEM. 

Small  arteries  from  the  circle  of  Willis  and  from  the  cere- 
bral arteries  near  the  circle  constitute  this  system.  It  is 
made  up  of  six  groups  of  vessels: 

(1)  Antero-median  Granglionic. — They  rise  from  the  an- 
terior cerebral  arteries  and  anterior  communicating.  Piercing 
the  lamina  cinerea  (and  a  few  of  them,  the  anterior  perfo- 
rated lamina)  they  supply  the  bulb  of  the  caudate  nucleus 
and  anterior  wall  of  the  third  ventricle. 

(24)    Artera  cerebri  posterior.  (25)    A.  basilaris. 


THE    GRAY   AND    WHITE     MATTER.  97 

(2,  3)  The  Antero-lateral  Ganglionic  Arteries  take  their 
origin,  on  either  side,  from  the  middle  cerebral  artery,  a  little 
outside  the  circle  of  Willis.  They  pierce  the  anterior  perfo- 
rated lamina  and  are  distributed  to  the  striate  body,  internal 
capsule  and  optic  thalamus.  One  of  this  group  is  the  len- 
ticulo-striate  artery.  It  supplies  almost  the  entire  corpus 
striatum.  On  account  of  its  frequent  rupture,  it  is  called 
the  artery  of  cerebral  hemorrhage  ( Charcot) . 

(4)  Postero-median  Ganglionic. — These  are  branches  of 
the  posterior  cerebral  and  posterior  communicating  arteries. 
They  supply  the  interpeduncular  structures  and  crustae ;  and 
(after  piercing  the  posterior  perforated  lamina)  the  walls  of 
the  third  ventricle  and  medial  parts  of  the  optic  thalami. 

(5,  6)  Postero-lateral  Ganglionic  Arteries. — They  rise, 
on  either  side,  from  the  posterior  cerebral  artery  after  it  has 
wound  around  the  crusta.  They  are  distributed  to  the  pos- 
terior part  of  the  optic  thalamus,  the  geniculate  bodies  and 
corpora  quadrigemina. 

The  ganglionic  arteries  pass  to  their  distribution  without 
communicating  with  one  another  or  with  the  cortical  arteries. 
They  are  end-arteries  of  Cohnheim.  Between  the  cortical 
and  ganglionic  systems,  there  is  an  area:^  poorly  supplied  with 
blood.    That  is  the  area  of  cerebral  softening. 

Choroid  Arteries.^^ — They  are  three  in  number. 

Anterior  Choroid. — Coming  from  the  internal  carotid  ar- 
tery, the  anterior  choroid  artery^^  enters  the  apex  of  the 
descending  horn  of  the  lateral  ventricle;  and  supplies  the 
inferior  two-thirds  of  the  choroid  plexus,  a  part  of  the  velum 
interpositum,  the  hippocampus  major  and  corpus  fimbriatum. 

The  Postero-lateral  ChoroidJ^^  is  a  branch  of  the  posterior 

(26)  Arterise  choroidese. 

(27)  Arteria  choroidea  anterior.  :  , 

(28)  A.  choroidea  postero-lateralis.  I   ; 


98  THE    BRAIN   AND    SPINAL    CORD. 

cerebral.    It  is  distributed  to  the  upper  third  of  the  choroid 
plexus  of  the  lateral  ventricle  and  to  the  velum  interpositum. 

Poster o-medial  Choroid?^ — ^Also  a  branch  of  the  posterior 
cerebral  artery,  it  supplies  the  choroid  plexuses  of  the  third 
ventricle;  and,  with  branches  from  the  superior  cerebellar, 
completes  the  supply  of  the  velum  interpositum.  The  pos- 
tero-lateral  and  postero-medial  choroid  vessels  have  their 
origin,  course  and  distribution  wholly  within  the  great  trans- 
verse and  choroid  fissures. 

Veins.3^ — ^The  velum  interpositum  and  lateral  and  third 
ventricles  are  drained  by  the  common  vein  of  Galen.^^  The 
veins  of  Galen  (Vv.  cerebri  intemse)  are  formed,  one  on 
either  side,  at  the  foramen  of  Monro,  by  the  union  of  the 
veins  of  the  striate  body^^  q^^^  choroid  vein  and  receive  the 
basilar.33 

The  Supenor  Cerebral  Veins,^^  eight  to  twelve  in  number, 
carry  away  the  blood  from  the  superior  surface  of  the  hemi- 
sphere. They  run  obliquely  upward  and  forward  into  the 
superior  longitudinal  sinus.^^  Just  before  emptying  into  the 
sinus  they  receive  most  of  the  medial  veins.^^ 
,  The  Medial  Cerebral  Veins. — They  drain  the  medial  sur- 
face of  the  hemisphere.  The  veins  of  that  surface  which  do 
not  empty  into  the  superior  cerebral  veins  unite  and  form  the 
inferior  longitudinal  sinus-^*^ 

The  base  of  the  cerebrum  and  border  of  its  convex  surface 
are  drained  by  the  Inferior  Cerebral  Veins. ^^    On  the  tento- 

(29)  Arteria   choroidea  postero-medialls. 

(30)  Venae. 

(31)  V.   cerebri  magna. 

(32)  V.  corporis  striati  (sing.). 

(33)  V.  choroidea. 

\     (34)  W.  cerebri  superiores. 

(35)  Sinus  sagittalis  superior. 

(36)  Vv.  cerebri  medlales.  ' 

(37)  Sinus  longitudinalis  inferiof. 

(38)  Vv.  cerebri  inferiores.  ' 


THE    GRAY    AND_WHITE    MATTER.  99 

rial  surface  of  the  hemisphere,  these  veins  empty,  against  the 
current,  into  the  lateral  and  superior  petrosal  sinuses.^^ 
Those  from  the  temporal  and  frontal  lobes  empty  into  the 
cavernous  sinus,^^  excepting  the  small  anterior  cerebral  vein 
and  the  deep  Sylvian  vein,  which  unite  with  the  inferior 
striate  veins  in  forming  the  basilar.  The  basilar  vein  receives 
additional  blood  from  the  interpeduncular  structures,  the 
uncinate  gyrus  and  the  middle  horn  of  the  lateral  ventricle 
and  from  the  mid-brain  as  it  winds  around  it  to  empty  into 
the  corresponding  vein  of  Galen  near  its  termination.  In  or 
near  the  fissure  of  Sylvius  there  are  two  inferior  cerebral 
veins  of  large  size:  The  middle  cerebral  vein/'^  which  runs 
from  the  under  surface  of  the  temporal  lobe,  medialward, 
along  the  fissure  of  Sylvius  to  the  cavernous  sinus;  and  the 
great  anastamotic  vein  of  Trolard,  whose  course  is  much 
the  same,  but  in  front  of,  the  Sylvian  fissure.  Rising  on  the 
parietal  lobe,  it  winds  inward  along  the  lesser  wing  of 
the  sphenoid  bone  to  the  anterior  extremity  of  the  cavernous 
sinus.  The  main  trunks  of  all  the  cerebral  vessels  are  con- 
tained in  the  pia  mater. 

There  are  no  lymphatic  vessels  in  either  the  brain  or  spinal 
cord;  perivascular  lymph  spaces  carry  the  fluid  from  the 
interior  to  the  subarachnoid  spaces. 

(39)  Sinus  transversus  and  S.  petrosus  superior. 

(40)  Sinus  cavernosus. 

(41)  Vena  cerebri  media. 


CHAPTER  V. 


HIND-BRAIN. 
Section  I.     The  Cerebellum. 

The  hind-brain  is  composed  of  the  cerebellum  and  the  pons. 
The  cerebellum  is  the  dorsal  portion  of  the  hind-brain.  It  is 
called  the  little  brain.  Its  weight  is  about  five  ounces, 
slightly  more  than  one- tenth  of  the  whole  brain.  It  is  situ- 
ated in  the  posterior  fossa  of  the  skull,  under  the  tentorium 
cerebelli  and  dorsal  to  the  pons  and  medulla  oblongata.  Be- 
tween it  and  the  last  two  structures  is  inclosed  the  fourth 
ventricle.^ 

Function. — The  cerebellum  is  an  important  way-station, 
or  relay,  in  the  indirect  motor  and  indirect  sensory  paths.  In 
response  to  impulses  received  from  skin,  muscles,  tendons, 
joints  and  viscera,  it  is  also  believed  to  originate  impulses 
which  co-ordinate  muscles  and  maintain  equilibrium.  More- 
over, according  to  Russell,  each  cerebellar  hemisphere  exer- 
cises an  important  inhibitory  function,  through  the  superior 
peduncles,  upon  the  opposite  side  of  the  cerebrum.  Divi- 
sions.— The  cerebellum  is  made  up  of  two  lateral  parts,  the 
hemispheres,^  and  a  central  part,  uniting  the  hemispheres 
together,  called  the  vermis  cerebelli,  or  worm. 

The  Cerebellar  Hemispheres  measure  two  inches  from  be- 
fore backward  and  about  the  same  in  thickness,  antero- 
medially;  but  they  taper  rapidly  toward  the  lateral  borders. 

(1)  Ventriculus  quartus.  .  ,  ,     ,       , 

(2)  Ke^nlsphuerium  ceretelli.    '.   /   -  ,  /  '<■  \    ' 


HIND-BRAIN.  lOI 

They  are  joined  together  by  the  worm,  which  forms  the  most 
elevated  part  of  the  cerebellum. 

The  vermis,  or  worm,  is  a  small  elongated  lobe,  shorter 
and  much  thinner  than  the  hemisphere.  In  animals"  lower 
than  mammals,  it  is  the  only  part  of  the  cerebellum  present. 
Its  transverse  ridges  give  it  a  worm-like  appearance.  It 
unites  the  upper  half  of  the  medial  aspect  of  the  hemispheres, 
their  lower  halves  being  separated  by  an  antero-posterior 
groove,  called  the  valley,  or  vallecula.^  The  upper  surface  of 
the  vermis  is  called  the  superior  worm,  or  vermis  superior; 
and  the  lower  surface,  the  inferior  worm,  or  vermis  inferior. 
The  superior  and  inferior  surfaces  are  separated  from  one 
another  at  the  posterior  end  of  the  worm  by  the  great  hori- 
zontal fissure;*  anteriorly,  the  medullary  body^  of  the  cere- 
bellum separates  them.  At  either  end  of  the  worm  is  a  notch 
bounded  by  the  vermis  and  the  hemispheres,  the  anterior  and 
posterior  cerebellar  notches. 

The  posterior  cerebellar  notch,  incisura  cerebelli  posterior, 
is  occupied  by  the  falx  cerebelli.  A  prolongation  of  the 
medullary  body  of  the  cerebellum  issues  from  the  incisura 
cerebelli  anterior,  or  anterior  cerebellar  notch. 

The  Medullary  Body  splits,  in  its  medial  part,  into  two 
laminae:  a  superior,  which  forms  the  superior  medullary  ve- 
lum and  three  pairs  of  peduncles,  and  an  inferior,  which 
is  the  inferior  medullary  velum.  Separating  at  an  acute 
angle,  the  two  laminae  form  the  tent  and  lateral  recesses  of 
the  fourth  ventricle. 

The  inferior  medullary  velum^  is  the  inferior  lamina  of 
the  medullary  body.    It  is  a  short  plate  of  white  matter,  not 

(3)  Vallecula  cerebelli. 

<4)  Sulcus  horizontalis  cerebelli. 

(5)  Corpus  medullare. 

(6)  Velum  medullare  poaterius. 


102  THE    BRAIN   AND    SPINAL    CORD. 

more  than  a  quarter  of  an  inch  long.  It  ends  in  a  concave 
border  from  which  a  sheet  of  epithelium  continues  down  over 
the  fourth  ventricle;  and  together  they  form  the  inferior 
half  of  the  roof  of  that  cavity.  Laterally,  the  inferior  velum 
extends  to  the  flocculus  of  the  hemisphere,  and  blends  with 
the  middle  cerebellar  peduncle.  Of  the  worm  it  covers  the 
nodulus,  antero-superiorly.  It  bounds,  dorsally,  the  lateral 
recesses  of  the  fourth  ventricle. 

The  Superior  Lamina  of  the  Medullary  Body  joins  the  cere- 
bellum immediately  to  the  pons.  The  superior  lamina  is 
made  up  of  three  pairs  of  cerebellar  peduncles  and  the  supe- 
rior medullary  velum.'''  They  are  the  prolongations  of  the 
white  matter  which  constitutes  the  corpus  medullare  of  the 
cerebellum. 

The  superior  peduncles  (crura  ad  cerebrum,  or  brachia 
conjunctiva)  converge  as  they  pass  forward  and  upward  to 
the  inferior  quadrigeminal  bodies,  where  they  disappear. 
They  are  joined  to  one  another  by  a  thin  plate  of  white 
matter,  the  superior  medullary  velum,  or  valve  of  Vieussens; 
with  the  valve,  they  form  the  dorsal  longitudinal  fibers  of 
the  pons ;  and,  as  such,  the  roof  and  lateral  boundaries  of  the 
superior  half  of  the  fourth  ventricle.  Beneath  the  corpora 
quadrigemina  and  aqueduct  of  Sylvius,  most  of  the  fibers  of 
the  superior  cerebellar  peduncles  decussate,  and  pass  into  the 
hypothalamic  region  of  the  opposite  side.  They  end  chiefly 
in  the  red  nucleus,  which  they  surround. 

The  inferior  peduncles  of  the  cerebellum  (crura  ad  niedul- 
1am)  8  issue  from  the  cerebellum  between  the  superior  and 
middle  peduncles.  They  first  run  ventrally  to  the  dorsal 
surface  of  the  pons,  near  the  posterior  border;  and  then, 
bending  downward  and  backward  (a  flexion  of  more  than  90 

(7)    Velum  medullare  anterius.  (8)    Corpora  restlformia. 


HIND-BRAIN.  IO3 

degrees),  they  converge  in  the  posterior  areas  of  the  medulla 
toward  the  calamus  scriptorius.  They  help  to  form  the  floor 
and  to  bound  laterally  the  inferior  half  of  the  fourth  ven- 
tricle.   In. the  medulla  they  are  called  the  restiform  bodies. 

The  middle  peduncles  (crura  ad  pontem)^  join  the  cere- 
bellum to  the  lateral  borders  of  the  pons.  They  are  con- 
tinuous with  the  ventral  (or  superficial)  transverse  and  the 
middle  transverse  fibers  of  the  pons.  The  middle  peduncles 
are  external  to  the  superior  and  inferior  peduncles,  and  are 
opposite  the  widest  part  of  the  fourth  ventricle. 

Great  Horizontal  Fissure. — The  cerebellum  has  one  great 
fissure  which  divides  it  into  upper  and  lower  surface.  The 
sulcus  horizontalis  cerebelli  is  shaped  like  a  horseshoe;  its 
extremities  are  located  on  either  side  of  the  medullary  body, 
from  which  the  fissure  runs  backward,  dividing  the  border  of 
each  hemisphere  and  the  posterior  end  of  the  worm.  In  the 
great  horizontal  fissure  the  remaining  important  fissures  of 
the  cerebellum  terminate.  They  are  nearly  parallel  with  one 
another;  hence,  the  cerebellum  is  laminated,  not  convoluted 
like  the  cerebrum.  The  extremities  of  the  great  horizontal 
fissure  are  separated  from  the  fourth  ventricle  by  a  sheet  of 
epithelium,  on  either  side,  uniting  the  borders  of  the  superior 
and  inferior  medullary  laminae,  and  bounding  externally  the 
lateral  recesses.  When  the  cerebellum  is  separated  from  the 
pons  and  medulla  it  presents  along  its  anterior  border  be- 
tween superior  and  inferior  medullary  laminae  the  transverse 
fissure. 

SUPERIOR  SURFACE  OF  THE  CEREBELLUM. 

The  superior  surface^^  of  the  cerebellum  is  bounded  by  the 
great  horizontal  fissure  and  the  superior  lamina  of  the  medul- 

(9)    Brachia  pontis.  (10)    Fades   cerebelli   superior. 


104  THE    BRAIN    AND    SPINAL    CORD. 

latry  body.     It  is  divided  into  five  continuous  lobes  by  four 
crescentic  fissures,  called  interlobular  fissures.^^ 

Fissures. — ^The  interlobular  fissures  divide  the  worm  and 
both  hemispheres;  and  each  lobe  is  composed  of  a  central 
and  two  lateral  portions,  called  lobules.  These  fissures  are 
named  in  accordance  with  their  relations  to  the  lobules  in  the 
worm,  viz.: 

(1)  The  Preceiitral  Fissure}^  which  is  located  in  the  an- 
terior cerebellar  notch.  It  is  between  the  lingula  and  lobulus 
centralis,  in  the  worm;  between  the  fraenulum  and  ala,  in 
the  hemisphere. 

(2)  The  Postcentral  Fissure}^  in  the  worm,  separates  the 
lobulus  centralis  from  the  culmen;  and,  in  the  hemisphere, 
the  ala  from  the  anterior  crescentic  lobule.  The  fissure  fol- 
lows the  anterior  border  of  the  superior  surface.  Both  cen- 
tral fissures  terminate  on  the  dorsum  of  the  superior  medul- 
lary lamina. 

(3)  Preclival  Fissure. — Behind  the  culmen  and  anterior 
crescentic  lobules  is  the  preclival  fissure.  It  bounds  the  clivus 
and  posterior  crescentic  lobules  in  front.  It  ends  at  the  junc- 
tion of  the  anterior  and  middle  thirds  of  the  antero-lateral 
border  in  the  great  horizontal  fissure. 

(4)  The  PostcUval  Fissure  is  located  in  the  posterior  cere- 
bellar notch,  from  which  it  curves  outward  and  forward  in  the 
superior  surface  of  the  hemispheres.  It  separates  the  clival 
lobe  from  the  folium  cacuminis,  in  the  worn!,  and  the  postero- 
superior  lobules  in  the  hemispheres.  It  ends  in  the  horizontal 
fissure  at  the  junction  of  the  posterior  and  middle  thirds  of 
the  antero-lateral  border. 

(11)  Pissurse  interlobulares. 

(12)  Sulcus  prsecentralis  cerebelU. 

(13)  Sulcus  postcentralis. 


HIND-BRAIN. 


[05 


Fissures  and  lobules  of  the  upper  surface  of  the  cerebellum 
from  before  backward: 


Hemisphere. 
Frsenulum. 

Ala. 

Anterior  crescentic. 

Posterior  crescentic 

Postero-superior. 


Worm. 
Lingula. 
Precentral  fissure. 
Lobulus  centralis. 
Postcentral  fissure. 
Culmen. 

Preclival  fissure. 
Clivus. 

Post  clival  fissure. 
Folium  cacuminis. 
Great  horizontal  fissure. 


Hemisphere. 

Fraenulum. 

Ala. 

Anterior  crescentic. 

Posterior  crescentic. 

Postero-superior. 


Lobes  of  Superior  Surface. — ^These  include  the  divisions 
of  the  worm  and  of  the  hemispheres,  and  are  five  in  number. 

Lingula  and  Frcenula  (Lobus  lingulaB). — The  lingula^  ^  is 
a  very  small  lobule  of  the  vermis  entirely  concealed  in  the 
anterior  cerebellar  notch  by  the  overhanging  central  lobule. 
It  is  a  tongue-shaped  group  of  four  or  five  rudimentary  trans- 
verse laminae.  It  rests  upon  the  superior  medullary  velum, 
with  which  its  white  center  is  continuous.  Laterally,  the 
lingula  tapers  off  and ,  is  represented,  if  at  all,  in  the  hemi- 
sphere by  a  very  thin  folium  called  the  fraenulum.i^  Thf3 
frgenulum  is  bounded  by  the  superior  cerebellar  peduncle 
in  front,  and  by  the  precentral  fissure  behind.  The  pre- 
central fissure  separates  the  lobp  of  the  lingula  from  the  cen- 
tral lobe. 

Central  Lohule  and  Alee  (Lobus  centralis). — The  lobulus 
centralis  is  situated  between  the  precentral  and  postcentral 
fissures,  in  the  anterior  cerebellar  notch.  It  covers  the  lin- 
gula and  in  turn  is  overhung  by  the  culmen.     Four  or  five 

(14)    Lingrula  cerebelll.  (15)    Vinculum  Ungnlse  cerebelli. 


I06  THE    BRAIN    AND    SPINAL    CORD. 

small  transverse  laminaB  make  it  up.  On  sagittal  section, 
it  is  seen  to  form  a  single  branch  of  the  corpus  trapezoides 
(arbor  vitae).  The  laminae  of  the  central  lobule,  continuing 
into  either  hemisphere,  form  a  triangular  or  wing-like  lobule, 
the  ala  (ala  lobuli  centralis). 

Oulmen  and  Anterior  Crescentic  Lohules  (Lobus  culminis). 
— In  the  culmen^^  the  surface  of  the  cerebellum  reaches 
its  highest  elevation.  It  is  a  large  lobule  and  occupies  more 
than  half  of  the  upper  surface  of  the  worm.  It  is  made  up 
ot  three  or  four  prominent  laminae,  which  extend  laterally 
into  the  hemispheres;  and,  there,  form  the  anterior  cres- 
centic lobules.i"^  The  latter  occupy  about  one-third  of  the 
upper  surface  of  the  hemispheres.  The  preclival  fissure  sepa- 
rates the  culmen  and  anterior  crescentic  lobules  (the  lobe 
of  the  culmen)  from  the  clival  lobe. 

Clivus  and  Posterior  Crescentic  Lohules  (Lobus  clivi). — 
The  clivus^  ^  forms  the  posterior  slope,  as  the  culmen  forms 
the  summit,  of  the  monticulus  cerebelli.  The  clivus  has 
about  half  the  extent  of  the  culmen.  Its  laminae  are  con- 
tinued into  either  hemisphere,  where  they  form  the  large 
posterior  crescentic  lobule.^^  The  increased  size  in  the 
hemisphere  is  due  to  the  expansion  of  the  secondary  folia 
found  in  the  worm.  The  anterior  and  posterior  crescentic 
lobules  constitute  the  quadrate  lobe,^^  which  forms  the  an- 
terior two-thirds  of  the  superior  surface  of  the  hemisphere. 
The  clivus  and  its  hemispherical  extensions  are  inclosed 
between  the  preclival  and  postclival  fissures. 

The    Folium    Cacuminis    and    Postero-superior    Lohules 


(16)  Culmen  monticull   cerebelli. 

(17)  Pars  anterior  lobuli  quadrangularls. 

(18)  Declive  monticull    cerebelli. 

(19)  Pars  posterior  lobuli  quadrangrularis. 

(20)  Lobus  quadrangularis. 


HIND-BRAIN.  10/ 

(Lobus  cacuminis)  lie  behind  the  postclival  and  in  front  of 
the  great  horizontal  fissure.  The  folium  cacuminis^^  is  the 
terminal  lamina  in  the  superior  worm,  and  occupies  the  pos- 
terior cerebellar  notch.  It  is  beset  with  rudimentary  folia, 
which  are  largely  developed  in  the  hemispheres.  The  postero- 
superior  lobule^^  is,  therefore,  very  large  in  comparison  with 
the  folium  cacuminis.  It  expands  lateralward  to  the  postero- 
lateral border  of  the  hemisphere,  which  it  forms.  It  com- 
prises the  posterior  third  of  the  hemisphere's  superior  surface. 

INFERIOR  SURFACE  OF  THE  CEREBELLUM. 

The  inferior  surface  of  the  cerebellum^s  is  prominent 
laterally  and  depressed  centrally  (as  the  organ  is  view^ed 
inverted),  the  hemispheres  being  separated  by  the  antero- 
posterior groove,  called  the  vallecula?"^  The  valley  is  occu- 
pied by  the  inferior  worm  and  is  bounded  on  either  side  by 
a  small  fissure,  between  the  worm  and  the  overhanging  hemi- 
sphere, called  the  sulcus  valleculce.  The  inferior  cerebellar 
surface  is  limited  by  the  great  horizontal  fissure  and  the 
medullary  body  of  the  cerebellum.  It  is  more  complex  than 
the  superior  surface ;  and  its  fissures  are  more  sharply  curved 
forward  as  they  pass  from  the  worm  into  the  hemispheres. 

Fissures  of  Lower  Surface. — The  interlobular  fissures  of 
this  surface  are  very  deep.  They  are  three  in  number, 
namely : 

(1)  The  Postnodular  Fissure  is  in  the  anterior  end  of  the 
worm  between  the  nodule  and  uvula.  In  the  hemisphere  it 
winds  forward  and  outward  between  the  inferior  medullary 
velum  and  the  tonsil,  and  then  continues  lateralward  between 


(21)  Folium  vermis. 

(22)  Lobulus   semilunaris   superior. 

(23)  Facies   cerebelli  inferior. 

(24)  Vallecula  cerebelli. 


io8 


THE    BRAIN   AND   SPINAL    CORD. 


flocculus  and  digastric  lobule  to  the  anterior  end  of  the  great 
horizontal  fissure. 

(2)  The  Prepyr amidol  Fissure,  between  the  uvula  and 
pyramid,  is  very  concave  in  the  hemispheres.  It  curves  out- 
ward and  forward  around  the  tonsil,  separating  it  from  the 
digastric  lobule.  It  terminates  behind  the  flocculus  in  the 
postnodular  fissure. 

(3)  The  Post  pyramidal  Fissure,  between  the  pyramid  and 
tuber  valvulae,  is  near  the  posterior  end  of  the  worm.  It 
forms  an  oblique  groove  in  either  sulcus  valleculas,  from 
which  three  concentric  fissures  extend  into  the  hemispheres. 
The  anterior  of  the  three  (the  pregracile),  usually  consid- 
ered the  postpyramidal  fissure  in  the  hemisphere,  separates 
the  digastric  lobule  from  the  postero-inferior  lobule;  the 
remaining  two  (midgracile  and  poetgracile)  subdivide  the 
postero-inferior  lobule  into  anterior  and  posterior  slender 
and  inferior  semilunar  sub-lobules.  The  last  is  bounded 
]>ehind  by  the  great  horizontal  fissure. 

Fissures  and  lobules  of  the  lower  surface  of  the  cerebellum, 
from  before  backward : 


Hemisphere. 
Flocculus. 

Tonsil. 

Digastric  lobule. 

Postero-inferior 
lobule. 


Worm. 
Nodule. 
Postnodular  fissure. 

Uvula. 
Prepyramidal  fissure. 

Pyramid. 
Postpyramidal  fissure. 
Tuber  valvulae. 

Oreat  horizontal  fissure. 


Hemisphere. 

Flocculus. 

Tonsil. 

Digastric  lobule. 

Postero-inferior 
lobule. 


Lobules  of  Lower  Surface. — ^They  are  not  continuous  with 
one  another  from  the  worm  to  the  hemisphere  as  on  the 


HIND-BRAIN.  lOQ 

upper  surface.  Excepting  the  posterior  lobules,  only  a  small 
ridge  beneath  the  sulcus  valleculas  joins  them  together.  The 
inferior  lobes  are  four  in  number.  Each  is  composed  of  a 
central  and  two  lateral  lobules.  The  lobule  in  the  worm 
gives  the  name  to  the  lobe, 

Nodulus  and  Flocculi  (Lobus  noduli). — The  nodule^^  is 
a  small  lobule  at  the  anterior  end  of  the  inferior  worm.  It 
is  composed  of  three  or  four  laminae,  which  project  from  the 
middle  of  the  lower  surface  of  the  inferior  medullary  velum. 
It  comprises  a  single  branch  of  the  arbor  vitas.  Though 
larger,  it  is  the  counterpart  of  the  lingula  on  the  superior 
velum.  It  is  bounded  by  the  sulcus  valleculae  on  either  side. 
The  inferior  medullary  velum  extends  laterally  from  the 
nodule,  and  blends  with  the  middle  peduncle  of  the  cere- 
bellum. In  front  of  the  tonsil,  a  fold  of  gray  matter 
(peduncle  of  flocculus) ^^  appears  on  the  velum.  That  gray 
matter  enlarges  more  externally  to  a  tufted  mass,  called  the 
flocculus.  The  flocculus  is  separated  from  the  tonsil  and 
digastric  lobule  by  the  postnodular  fissure.  The  whole  line 
of  structures,  namely,  the  nodule,  velum,  peduncle  and  floc- 
culus, form  the  lobe  of  the  nodule. 

Uvula  and  Tonsils  (Lobus  uvulae). — ^The  uvula^'^  com- 
prises a  considerable  part  of  the  vermis  inferior  behind  the 
nodule.  It  broadens  backward  and  is  widest  next  the  pyra- 
mid. Bounded  on  either  side  by  the  sulcus  valleculae,  it 
projects  into  the  valley  like  the  uvula  into  the  isthmus  of  the 
fauces.  Three  moderate  sized  laminae  and  six  or  eight  small 
folia  make  up  the  uvula.  A  slight  ridge,  the  furrowed  hand, 
joins  it  to  the  tonsiPs  in  the  hemisphere.  From  the  furrowed 
band  the  tonsil  expands  downward  and  backward,  forming  a 
lobule  of  nearly  a  dozen  sagittal  laminae.     The  tonsil   (or 

(25)  Nodulus  vermis.  (27)    Uvula  vermis. 

(26)  Pedunculus  flocculi.  (28)    Tonsilla  cerebelli. 


no  THE    BRAIN    AND    SPINAL    CORD. 

amygdala)  overhangs  the  side  of  the  uvula  and  conceals  the 
furrowed  band,  medially;  and,  behind,  it  conceals  the  con- 
necting ridge  between  the  pyramid  and  digastric  lobule.  The 
fossa  containing  the  tonsil  is  the  bird's  nest  (nidus  avis). 
Behind  the  uvular  lobe,  composed  of  the  above  three  lobules, 
are  the  prepyramidal  fissure  and  the  lobe  of  the  pyramid. 

Pyramid  and  Digastric  Lohules  (Lobus  pyramidis). — As 
seen  from  the  surface,  three  or  four  distinct  laminae  make 
up  the  pyramid,29  which  is  the  most  prominent  lobule  of  the 
inferior  worm.  A  low  connecting  ridge  joins  the  pyramid 
to  the  digastric  lobule  in  the  hemisphere.  The  digastric 
(or  biventral)  lobule^^  is  triangular  in  outline.  Its  base 
looks  toward  the  flocculus  and  is  bounded  by  the  postnodular 
fissure;  its  apex  is  continuous  with  the  connecting  ridge. 
The  laminae  composing  it  radiate  from  the  apex  toward  the 
base,  and  are  divided  into  two  groups  by  a  very  deep  intra- 
lobular fissure.  The  postpyramidal  fissure  bounds  it  postero- 
extemally,  and  separates  it  from  the  postero-inferior  lobule. 

Tuber  Valvulce  and  Postero-inferior  Lohules  (Lobus  tu- 
beris). — The  tuber  valvulae^^  forms  the  posterior  end  of  the 
inferior  worm.  It  resembles  the  lobules  of  the  vermis  su- 
perior, because  its  half  dozen  tertiary  laminae  are  continued 
into  the  hemispheres,  the  sulcus  valleculae  not  cutting  them 
off.  The  great  horizontal  fissure  separates  it  from  the  folium 
cacuminis  of  the  superior  worm.  The  postero-inferior  lobule^^ 
comprises  the  posterior  two-thirds  of  the  inferior  surface  of 
each  hemisphere,  extending  from  the  digastric  lobule  to  the 
postero-lateral  border.  Twelve  to  fifteen  laminae  compose 
the  lobule.    They  are  divided  into  three  groups  by  the  mid- 

(29)  Pyramis   vermis. 

(30)  liObulus  biventer. 

(31)  Tuber  vermis. 

(32)  Lobulus  semilunaris  inferior. 


HIND-BRAIN.  Ill 

gracile  and  postgracile  fissures;  the  groups  are  named  the 
anterior  slender,  or  pregracile,  posterior  slender,  or  post- 
gracile, and  inferior  semilunar.  The  inferior  semilunar  sub- 
lobule,  only,  is  continuous  with  the  laminse  of  the  tuber. 


GRAY  MATTER  OF  THE   CEREBELLUM. 

The  gray  matter  of  the  cerebellum  is  composed  of  cortex 
which  covers  the  cerebellar  laminae  and  of  ganglia  imbedded 
in  the  medullary  center. 

1.     Cortical  Gray  Matter. 

The  cortex  of  the  cerebellum  (substantia  corticalis)  is 
made  up  of  two  microscopic  layers,  viz.,  (1)  a  superficial, 
molecular,  or  gray  cellular  layer,  and  (2)  a  deep,  nuclear,  or 
rust-colored  granular  layer. 

(1)  Superficial,  Molecular,  or  Gray  Cellular  Layer. — 
Thickest  on  the  laminae  and  thinnest  beneath  the  fissures, 
this  layer  contains  small  spheroidal,  or  stellate,  cell-bodies 
with  their  processes,  and  large  flask-like  cell-bodies  with  their 
dendrites  and  axoijes  (the  cells  of  Purkinje)  and  a  close 
network  of  fibers. 

Cells. — The  bodies  of  Purhitijes  cells  are  located  near  the 
deep  surface  of  the  cellular  layer  (stratum  gangliosum). 
Bach  has  one  axone  which,  after  piercing  the  granular  layer, 
becomes  a  fiber  of  the  medullary  center  (a  projection  fiber). 
From  the  outer  end  of  each  cell-body  antler-like  processes, 
the  dendrites,  are  given  off;  they  rajnify  toward  the  surface 
in  a  plane  at  right  angles  to  the  intralobular  fissures.  The 
spheroidal  cell-bodies  form  an  outer  and  inner  layer.  They 
have  rich  dendritic  processes  and  one  axis-cylinder  each.  The 
dendrites  ramify  throughout  the  cellular  layer.  In  the  outer 
layer  the  stellate  cell-bodies  are  smaller  than  in  the  inner 


112  THE    BRAIN    AND    SPINAL    CORD. 

layer.  Their  axis-cylinders  run  parallel  with  the  surface  and 
at  right  angles  to  the  intralobular  fissures.  They  branch 
freely  and  terminate  in  a  manner  unknown.  The  inner  layer 
contains  the  'T)asket  cells."  Their  axis-cylinder  processes 
run  parallel  with  the  former,  and  give  off  vertical  branches 
which  descend  to  Purkinje's  corpuscles  and  inclose  them  in  a 
basket-work  of  filaments. 

Fibers  of  the  gray  cellular  layer  have  three  sources:  (a) 
The  dendritic  and  axonic  processes  of  neurones  within  the 
layer;  (b)  the  processes  of  cell-bodies  in  the  granular  layer. 
The  latter  comprise,  first,  the  neurogliar  fibers  of  Bergmann 
(vertical),  which  extend  from  the  granular  layer  outward 
to  the  surface  of  the  lamina,  where  they  form  a  feltwork 
like  the  limiting  membranes  of  the  retinas;  and,  second,  the 
axones  of  the  cell-bodies  in  the  granular  layer,  whose 
T-branches  run  parallel  with  the  interlobular  fissures  in  the 
superficial  layer,  (c)  The  fibers  of  the  medullary  center' 
(projection  fibers)  rise  or  end  largely  in  the  cellular  layer. 
The  axones  of  Purkinje's  neurones  compose  most  of  the  cen- 
trifugal projection  fibers.  The  centripetal  fibers,  which  rise 
either  in  other  parts  of  the  brain  or  in  the  spinal  cord  and 
ganglia,  terminate  in  end-tufts  or  moss-like  appendages 
(Cajal)  chiefly  in  the  superficial  layer. 

(2)  The  Deep,  Nuclear,  or  Rust-colored  Granular  Layer 
is  of  uniform  thickness.  It  blends  centrally  with  the  medul- 
lary body. 

Cells  of  the  Granular  Layer. — The  granules  are  small 
round,  or  stellate  cell-bodies,  largest  near  Purkinje's  cells, 
closely  packed  externally,  but  scattered  among  the  projection 
fibers  centrally.  Each  granule  has  one  axone.  It  runs  out 
into  the  cellular  layer,  branches  T-like,  and  forms  many  of 
the  tangential  fibers  of  that  layer.     Dendritic  processes  are 


HIND-BRAIN.  II3 

abundant.  They  ramify  chiefly  within  the  granular  layer. 
The  neurogliar  cell-bodies,  which  originate  the  vertical  fibers 
of  Bergniann,  lie  near  the  cells  of  Purkinje  (N.  8,  Add.). 

Among  the  fibers  of  the  granular  layer  are  included  the 
processes  of  the  granules  and  glia  cell-bodies,  and  the  effer- 
ent and  afferent  projection  fibers. 

The  functions  of  the  stellate  cells,  the  ^'basket  cells'^  and 
the  granule  cells  are  probably  receptive  and  associative;  they 
receive  impulses  through  the  centripetal  projection  fibers  and 
transfer  those  impulses  to  the  dendrites  or  bodies  of  Pur- 
kinje's  cells.  Purkinje's  cells  originate  impulses  for  the  co- 
ordination of  muscular  action  (Gordinier),  and  for  the  inhi- 
bition of  nervous  activity  in  the  opposite  cerebral  hemisphere 
(Eussell).  Hence  lesions  in  the  cerebellum  produce  inco- 
ordination, irritability  and,  rarely,  convulsions. 

II.     Ganglionar  Gray  Matter. 

The  ganglia  of  the  cerebellum  are  the  corpus  dentatum 
and  the  three  nuclei  of  Stilling. 

The  Corpus  Dentatum^  is  a  wavy,  sinuous  pouch  of  yellow- 
ish-brown gray  matter  imbedded  in  the  medullary  body  of 
each  hemisphere.  It  is  filled  with  white  fibers,  which  issue 
from  its  anterior,  open  end^  and  form  the  greater  part  of  the 
superior  cerebellar  peduncle.  Stellate  cell-bodies  (from  6 
microns  to  40  microns  in  diameter)  are  the  essential  element 
of  both  the  corpus  dentatum  and  Stilling's  nuclei. 

Nuclei  of  Stilling. — One  of  these,  a  club-shaped  mass,  the 
cork-like  nucleus  emboliformis,  partly  closes  thfe  hilus  of  the 
dentate  body.  Medial  to  that  is  an  elongated  antero-posterior 
ganglion,  bulbous  behind,  called  the  nucleus  glohosu^.  The 
third  nucleus  is  in  the  anterior  end  of  the  worm,  just  above 

(1)  Nucleus  dentatus. 

(2)  Hilus  nuclei  dentati. 


114  THE   BRAIN   AND    SPINAL   CORD. 

the  fastigium  of  the  fourth  ventricle.  It  is  called  the  nucleus 
of  the  highest  point  of  the  roof,  nucleus  fastigii.  In  the  two 
last  the  stellate  cell-bodies  are  larger  than  in  the  nucleus 
emboliformis  or  corpus  dentatum;  but,  otherwise,  they  are 
alike  in  structure.  The  nucleus  fastigii  and  nucleus  globosus 
form  the  terminal  station  for  the  acustico-cerebellar  tract, 
which  tract  sends  collaterals  to  the  nucleus  emboliformis  and 
corpus  dentatum.  In  this  manner  these  nuclei  are  associated 
with  the  vestibular  nuclei   (auditory)   of  the  opposite  side. 

V7HITE   MATTER   OF   THE    CEREBELLUM. 

The  white  matter  of  the  cerebellum  is  arranged  in  three 
systems  similar  to  that  of  the  cerebrum: 

I.     Projection,  or  peduncular,  fibers. 
II.     Commissural  fibers. 
III.     Association  fibers. 

I.     Projection  Fibers. 

These  include  all  fibers  of  the  medullary  body^  as  it  issues 
from  the  anterior  cerebellar  notch.  The  fibers  are  in  con- 
tinuity with  the  branches  of  the  medullary  body*  and  together 
constitute  the  arbor  vitce.  Dividing  medially  into  a  superior 
and  an  inferior  lamina  (united  laterally),  the  medullary 
body  forms  the  tent^  and  lateral  recesses^  of  the  fourth  ven- 
tricle. The  inferior  lamina  is  the  inferior  medullary  velum,'' 
whose  fibers  pass  into  the  nodule  and  fiocculi.  The  superior 
lamina  forms  the  superior  medullary  velum  and  three  pairs 
of  cerebellar  peduncles. 

Superior  Peduncles. — Two  bundles  of  fibers  maJ^e  up  the 

(3)  Corpus  medullare.  ,.      • 

(4)  Laminae  medullare  s. 
•     (5)    Fastigium. 

(6)  Recessus  lateralis  ventriculi  quarti. 

(7)  Velum  medullare  posterius. 


HIND  BRAIN.  Ilg 

superior  peduncles.^  They  are  afferent  and  efferent.  First, 
the  fibers  to  the  cerebrum  which  are  axones  of  cell-bodies 
situated  chiefly  in  the  corpus  dentatum,  but  which  axe  com- 
bined with  a  few  axones  of  Purkinje's  cells.  This  group  of 
fibers  ends  chiefly  in  the  opposite  red  nucleus,  where  the 
second  group  rises.  The  second  group,  rising  in  the  opposite 
red  nucleus,  ends  in  the  corpus  dentatum.  The  greater  num- 
ber of  fibers  in  the  superior  peduncles  decussate  in  the  teg- 
mentum. The  superior  medullary  velum^  arches  over  the 
fourth  ventricle  between  the  superior  peduncles.  It  is  com- 
posed chiefly  of  longitudinal  fibers  running  between  the  worm 
and  the  cerebrum.  One  distinct  bundle,  derived  from  the 
spinal  cord,  passes  through  it  to  the  worm.  It  is  the  antero- 
lateral ascending  cerebellar  tract  (Hoche).  The  decussating 
root-fibers  of  the  fourth  nerve  (trochlear)  course  transversely 
through  the  superior  velum,  also  certain  commissural  fibers 
of  the  hind-brain. 

Middle  Peduncles. — They  pass  to  the  pons  and  form  its 
ventral  and  middle  transverse  fibers.  They  also  are  both 
afferent  and  efferent.  The  fibers  of  the  middle  peduncle^  ^ 
rise,  first,  from  every  part  of  the  cerebellar  cortex.  They 
cross  one  another  in  the  peduncle,  fibers  from  the  anterior 
part  of  the  hemisphere  running  to  the  posterior  portion  of 
the  pons,  and  vice  versa.  Passing  toward  the  median  iine, 
the  fibers  end  in  the  nuclei  pontis  and  nuclei  of  the  formatio 
reticularis  on  both  sides  of  the  raphe.  Second,  the  remain- 
ing fibers  are  axones  of  cell-bodies  situated  mainly  in  the 
opposite  nucleus  pontis.  The  latter  form  a  segment  in  the 
indirect  motor  paths  contained,  above  the  pons,  in  the  medial 
and  lateral  fifths  and  the  intermediate  bundle  of  the  crusta 

(8)  Brachia  conjunctiva. 

(9)  Velum  medullare  anterlus. 

(10)  Brachium  pontis. 


Il6  THE    BRAIN   AND    SPINAL    CORD. 

Collaterals  from  both  groups  of  fibers  ascend  and  descend 
in  the  pons.  They  run  upward  with  both  crusts,  but  chiefly 
with  the  opposite  one;  and  they  accompany  the  fillet  and 
posterior  longitudinal  bundle  of  the  same  side  to  the  nuclei 
of  the  third,  fourth  and  sixth  cranial  nerves. 

The  Inferior  Peduncles  can  be  traced  to  the  upper  part  of 
the  hemispheres  and  to  the  worm.  Inferiorly,  they  become 
the  restiform  bodies^  ^  of  the  medulla  oblongata.  The  bun- 
dles of  component  fibers  are  very  numerous :  ( 1 )  The  direct 
cerebellar  tract,  whose  origin  is  in  Clark's  column  of  the 
cord  and  termination  in  the  superior  worm.  (2)  The  ex- 
ternal arciform  fibers  of  the  medulla  (posterior  and  anterior), 
which  rise  in  the  nucleus  gracilis  and  nucleus  cuneatus  and 
end  in  the  vermis  superior,  the  former  on  the  same  and  the 
latter  on  the  opposite  side.  (3)  The  acustico-cerebellar  tract 
from  the  nuclei  of  the  vestibular  nerve  to  the  opposite  nucleus 
fastigii  and  nucleus  globosus.  (4)  A  bundle  from  the  lateral 
nucleus  of  the  medulla  to  the  cerebellar  cortex  on  the  same 
side.  (5)  The  antero-lateral,  descending  cerebellar  tract, 
which  runs  from  the  cortex  of  the  cerebellum  to  the  anterior 
gray  horn  in  the  cord.  (6)  The  internal  arciform  fibers  to 
the  opposite  lower  olive,  the  cerebello-olivary  tract. 

Most  of  the  fibers  which  leave  the  cerebellum  by  way  of  the 
middle  and  inferior  peduncles  are  axones  of  Purkinje's  cells; 
they  connect  the  cerebellum  with  the  motor  nuclei  of  cranial 
and  spinal  nerves. 

II.     Commissural  Fibers. 
The  cerebellar  hemispheres  are  joined  by  transverse  fibers, 
of  which  there  are  two  sets,  namely:    One  near  the  anterior 
end  of  the  worm  beneath  the  central  lobe,  and  the  other  at 
the  posterior  end  of  the  worm. 

(11)    Corpus  restifarme  (singr.). 


HIND-BRAIN.  II7 

III.     Association  Fibers. 
Antero-posterior  fibers  join  the  cerebellar  laminae  to  one 
another.     They  arch  beneath  the  fissures,  and  remain  in  one 
hemisphere. 

BLOOD  SUPPLY  OF  CEREBELLUM. 

Three  pairs  of  arteries  supply  the  cerebellum.  The  supe- 
rior cerebellar,  from  the  basilar,  supplies  all  the  superior 
surface  except  a  narrow  zone  at  the  posterior  border;  and 
the  anterior  inferior  cerebellar,  also  from  the  basilar,  and 
the  posterior  inferior  cerebellar,  from  the  vertebral,  supply  the 
inferior  surface  and  the  posterior  part  of  the  superior  surface. 

The  superior  cerebellar  artery,  rising  from  the  basilar  just 
behind  the  posterior  cerebral,  from  which  it  is  separated  by 
the  oculomotor  nerve,  winds  dorsally  around  the  mid-brain 
and  distributes  branches  to  the  geniculate  bodies,  corpora 
quadrigemina,  velum  interpositum  and  dorsal  surface  of  the 
pons,  besides  the  vermis  superior  cerebelli  and  nearly  all  the 
superior  surface  of  the  hemisphere.  It  anastamoses  with 
both  the  inferior  cerebellar  arteries.  The  anterior  inferior 
cerebellar  is  given  off  by  the  basilar  near  its  origin.  It  runs 
lateral  ward,  behind  the  flocculus,  keeping  close  to  the  anterior 
border  of  the  hemisphere.  In  its  course  it  passes  anterior  to 
the  abducent  nerve  and  posterior  to  the  facial  and  auditory 
nerves.  The  posterior  inferior  cerebellar  artery  is  the  largest 
branch  of  the  vertebral  and  is  given  off  just  before  the  verte- 
bral arteries  unite  and  form  the  basilar.  Passing  first 
between  the  root-bundles  of  the  hypoglossal  nerve  and  then 
between  those  of  the  spinal  accessory  and  vagus  nerves,  the 
posterior  inferior  cerebellar  artery  bends  at  a  right  angle 
backward  and  runs  between  the  medulla  and  the  cerebellar 
hemisphere  where  it  divides  into  an  internal  and  an  external 


Il8  THE    BRAIN   AND    SPINAL    CORD. 

branch.  The  Internal  branch  follows  the  sulcus  valleculae 
and  gives  branches  to  the  medial  part  of  the  hemisphere  and 
the  vermis  inferior.  It  anastamoses  with  its  fellow  of  the 
opposite  side.  The  External  branch  runs  lateralward  from 
the  posterior  cerebellar  notch  over  the  inferior  surface  of  the 
hemisphere;  its  terminal  branches  wind  around  the  postero- 
lateral border  and  communicate  with  the  superior  cerebellar 
artery  on  the  upper  surface  of  the  hemisphere.  The  un- 
divided trunk  of  the  posterior  inferior  cerebellar  artery  gives 
small  branches  to  the  medulla  oblongata  and  supplies  the 
choroid  tela  of  the  fourth  ventricle. 

Three  sets  of  veins  carry  the  blood  away.  The  superior 
cerebellar  veins  pour  their  blood  against  the  current  into  the 
straight  sinus.  The  inferior  cerebellar  veins  empty  in  like 
manned  into  the  lateral  sinus;  and  the  lateral  cerebellar 
veins,  into  the  superior  petrosal  sinus. 

The  trunks  of  both  veins  and  arteries  ramify  in  the  pia 
mater. 

Lymphatics. — There  are  no  lymphatic  vessels  in  the  cere- 
bellum, but  the  perivascular  lymph  spaces  carry  out  the  lymph 
and  pour  it  chiefly  into  the  subarachnoid  space. 

Section  II.     The  Pons  Varolii. 

The  pons  is  the  ventral  part  of  the  hind-brain,  the  cere- 
bellum being  its  dorsal  portion.  The  pons  is  develpped  from 
the  floor  of  the  epencephalon.  It  is  so  named  because  it 
forms  the  connecting  link,  or  bridge,  between  the  mid-brain, 
above,  and  the  cerebellum  and  medulla  oblongata,  below; 
between  the  medulla  and  cerebellum,  and  between  the  two 
cerebellar  hemispheres. 

In  shape  the  pons  is  roughly  cylindrical.  A  coronal  section 
of  it  resembles  an  inverted  transverse  section  of  the  penis. 


HIND-BRAIN.  II9 

It  has  a  broad  basal  or  ventral  part^^  ^j^j  ^  narrow  dorsal 
portion.^  3 

Size. — The  pons  is  about  one  inch  long.  It  is  a  little 
broader  than  long,  and  measures  an  inch,  dorso-ventrally. 

Position. — It  rests  in  the  anterior  end  of  the  groove  which 
extends  from  the  foramen  magnum  to  the  dorsum  sellae,  and 
lies  between  and  ventral  to  the  hemispheres  of  the  cerebellum. 

Superiorly,  it  joins  the  mid-brain;  and,  behind,  it  is  con- 
tinuous with  the  medulla  oblongata. 

Surfaces  of  the  Pons. — The  pons  has  four  surfaces,  viz., 
superior  (attached)  ;  inferior  (attached)  ;  ventral  (free), 
and  dorsal  (free)  ;  and  two  borders,  namely,  right  and  left 
lateral,  continuous  with  the  middle  peduncles  of  the  cere- 
bellum.i* 

The  Superior  and  Inferior  Surfaces  are  made  by  section, 
and  are  directly  continuous  with  the  mid-brain  above  and 
the  medulla  below. 

Ventral  Surface  (Tuber  annulare). — The  ventral  surface 
of  the  pons  looks  downward  and  forward,  and  rests  on  the 
sphenoid  bone  behind  the  sella  Turcica.  It  is  divided  into 
lateral  halves  by  the  sulcus  basilaris,  containing  the  basilar 
artery.  Antero-posteriorly,  the  surface  is  slightly  convex, 
and  is  markedly  so  from  side  to  side.  It  shows  transverse 
striations,  which  converge  laterally,  due  to  the  fibers  that 
form  it,  and  enter  the  middle  peduncles  of  the  cerebellum. 
The  fibers  of  the  tuber  annulare  are  not  exactly  transverse  in 
direction.  Those  at  the  anterior  end  of  the  pons  are  arched, 
convex  forward,  and  form  a  rounded  margin,  which  covers 
the  lower  part  of  the  crustae  of  the  mid-brain;  at  the  pos- 
terior extremity  of  the  pons,  the  fibers  are  convex  backward 

(12)  Pars  basilaris  pontis.  (14)    Brachia  pontis. 

(13)  Pars  dorsalis  pontis. 


120  THE    BRAIN   AND    SPINAL    CORD. 

and  pfirtially  conceal  the  pyramids  of  the  medulla  oblongata. 
The  two  roots  of  the  5th  nerve  (trifacial) ^^  issue  from  the 
lateral  border  (Henle)  of  this  surface,  a  little  in  front  of  the 
middle. 

The  Dorsal  Surface  of  the  pons  is  concealed  by  the  cere- 
bellum. Medial  Portion. — It  presents  a  median  longitudinal 
elevation  due  chiefly  to  the  superior  peduncles  of  the  cere- 
bellum^^  and  valve  of  Yieussens}'^  The  peduncles  converge 
forward  and  upward  and  run  beneath  the  inferior  quadri- 
geminal  bodies  of  the  mid-brain.  The  valve  spans  the  in- 
terval between  the  peduncles  and  forms  the  floor  of  the  slight 
groove  which  separates  them.  A  low  and  narrow  ridge  runs 
from  the  corpora  quadrigemina  down  the  middle  of  the  valve. 
It  is  called  the  frenulum.  In  the  superior  medullary  velum 
(or  valve  of  Vieussens),  the  4th  cranial  nerve  (n.  trochlearis) 
decussates  and  issues  from  its  lateral  portion  on  each  side  of 
the  frenulum. 

Lateral  Portion. — Each  lateral  portion  of  the  dorsal  sur- 
face is  depressed.  On  this  depressed  portion,  the  lateral 
fillet^^  produces  a  low  ridge  which,  trending  upward  and 
toward  the  median  line,  winds  over  the  anterior  end  of  the 
superior  peduncle  and  terminates  at  the  inferior  corpus  quad- 
rigeminum.  This  ridge  is  joined  by  a  much  slighter  one, 
which  runs  from  the  valve  outward  and  forward  over  the 
posterior  end  of  the  superior  peduncle;  it  is  caused  by  a 
bundle  of  fibers  from  the  antero-lateral  ascending  cerebellar 
tract. 

WHITE   MATTER   OF   THE   PONS. 

The  pons  is  composed  of  transverse  and  longitudinal  white 
fibers  and  of  gray  matter.    The  transverse  fibers  are  found  in 

(15)  Nervus  trig-eminus.  (17)    Velum  meduHare  anterius 

(16)  Brachia  conjunctiva.  (18)    Lemniscus  lateralis. 


HIND-BRAIN.  121 

the  ventral  portioni^  of  the  pons;  the  longitudinal,  in  the 
dorsal  part,^^  and  also  intersecting  the  middle  transverse 
fibers. 

TRANSVERSE    FIBERS    OF    PONS. 

The  transverse  fibers  form  three  consecutive  layers  in  the 
ventral  area  of  the  pons,  viz.,  the  ventral,  the  middle,  and 
the  dorsal  layer.     They  lie  one  upon  another. 

The  Ventral  Transverse  Fibers  (superficial  transverse) 21 
form  a  thin  layer  constituting  the  tuber  annulare,  or  ventral 
surface  of  the  pons. 

Middle  Transverse  Fibers  (ventral  deep-transverse). — 
These  form  a  thick  lamina  dorsal  to  the  ventral  transverse 
fibers  and  in  contact  with  the  ventral  lamina.  They  are 
intermingled  with  longitudinal  fibers  running  from  the 
crustae  (middle  three-fifths)  down  to  the  pyramids  of  the 
medulla  oblongata  and  with  fibers  of  the  fronto-pontal,  inter- 
mediate and  temporo-pontal  tracts  which  end  in  the  pons. 
In  the  meshes  between  the  intersecting  fibers  are  masses  of 
gray  matter  called  the  nuclei  pontis.  The  middle  and  ventral 
transverse  fibers  form  the  middle  cerebellar  peduncles.22 
They  are  made  up  (1)  of  axones  of  Purkinje^s  cells  which 
end  in  the  nuclei  pontis  and  nuclei  of  the  formatio  reticu- 
laris on  both  sides  of  the  pons,  and  (2)  of  axones  of  cell- 
bodies  in  these  same  nuclei,  especially  the  nuclei  pontis,  which 
terminate  in  the  cerebellar  cortex  of  the  opposite  side; 

The  Dorsal  Transverse  Fibers  (dorsal  deep-transverse)  com- 
pose a  thin  layer  on  the  dorsum  of  the  middle  transverse  and 
pyramidal  fibers,  separating  them  from  the  formatio  reticu- 
laris. The  dorsal  transverse  lamina  is  best  marked  in  the 
posterior  part  of  the  pons,  where  it  is  called  the  trapezium. 

(19)  Pars  basilaris  pontis.  (21)    Fibrse  pontis  superflciales. 

(20)  Pars  dorsalis  pontis.  (22)    Brachia  pontis. 


122  THE    BRAIN   AND    SPINAL    CORD. 

The  trapezium  forms  the  boundary  between  the  dorsal  and 
ventral  areas  of  the  pons.  It  rises  chiefly  from  the  nuclei  of 
the  cochlear  nerve  and,  after  decussating  in  the  raphe,  is 
continued  up  in  the  lateral  fillet  to  the  corpus  quadrigeminum 
inferius.  A  few  fibers  join  the  tract  directly  from  the 
cochlear  nerve.  The  nuclei  of  the  trapezium,  of  superior 
olive  and  of  lateral  fillet  form  way-stations  for  a  number  of 
its  fibers.  The  trapezium  and  lateral  fillet  form  the  second 
stage  in  the  auditory  conduction  path,  the  auditory  im- 
pulses having  reached  the  trapezium  and  lateral  fillet  through 
the  auditory  nerve  are  continued  (a)  through  the  brachium 
inferius  and  (b)  the  acustic  radiations  to  the  temporal  cortex. 

LONGITUDINAL   FIBERS   OF   PONS. 

Like  the  transverse,  the  longitudinal  fibers  of  the  pons  are 
arranged  in  three  distinct  laminae,  viz.,  the  ventral,  the  middle 
and  the  dorsal.  The  last  two  are  in  contact  with  one  an- 
other in  the  dorsal  area^s  of  the  pons ;  but  the  ventral  lamina 
is  separated  from  the  middle  by  the  trapezium. 

The  Ventral  Longitudinal  Fibers  (ventral  deep-longitu- 
dinal) are  the  motor  fibers  of  the  crustae.  The  pyramidal 
fibers^*  run  from  the  middle  three-fifths  of  each  crusta  down 
through  the  middle  transverse  layer  of  the  pons  to  the  pyra- 
mids of  the  medulla  oblongata.  They  form  a  thick  bundle 
en  either  side  of  the  median  line,  which  presses  down  the 
ventral  transverse  fibers  and  produces  the  sulcus  basilaris. 
The  ventral  longitudinal  fibers  are  to  a  small  extent  made  up 
of  fibers,  probably  collaterals,  from  the  middle  cerebellar 
peduncles  (chiefly  from  the  opposite  one)  which  run  both 
toward  the  cerebrum  and  the  spinal  cord.  The  nuclei  pontis, 
one  on  either  side,  are  situated  among  them.    The  pyramidal 

(23)  Pars  doi:salis  pontis. 

(24)  Fasciculi   lon|ritudinales   pontis   (pyramidales). 


HIND-BRAIN.  I23 

tracts  diminish  in  size  during  their  descent,  because  of  the 
fibers  which  leave  them  to  decussate  and  end  in  the  nuclei  of 
motor  cranial  nerves. 

Middle  Longitudinal  Fibers  (dorsal  deep-longitudinal). — 
These  are  contained  in  the  formatio  reticularis.  They  are 
dorsal  to  the  trapezium,  and  lie  in  the  floor  of  the  fourth 
ventricle.  Laterally,  the  middle  lamina  is  in  contact  with 
the  dorsal  longitudinal  layer,  the  superior  peduncles  of  the 
cerebellum  lying  directly  on  it;  but,  medially,  the  two 
laminae  are  separated  from  one  another  by  the  fourth  ven- 
tricle. The  middle  longitudinal  fibers  are  mingled  with 
many  oblique  fibers ;  and,  thus,  there  is  produced  the  net-like 
arrangement  suggesting  the  name,  formatio  reticularis.  The 
formatio  reticularis  of  the  pons  is  continued  in  the  medulla 
oblongata.  Considerable  gray  matter  is  found  in  the  meshes, 
especially  in  the  part  next  the  fourth  ventricle.  The  latter 
contains  the  nuclei  of  the  fifth,  sixth  and  seventh  cranial 
nerves  and  a  part  of  the  nucleus  of  the  eighth  nerve.  The 
remaining  gray  matter  constitutes  the  nuclei  of  the  formatio 
reticularis,  etc.  In  the  formatio  reticularis  are  contained  six 
distinct  bundles  of  longitudinal  fibers:  The  fillet,  the  ante- 
rior and  the  posterior  longitudinal  bundle,  the  olivary  bundle, 
the  crossed  descending  tract  from  the  red  nucleus,  and  in  the 
lower  part  of  the  pons  the  ascending  root  of  the  trifacial 
nerve.  According  to  Hoche,  also,  the  antero-lateral  ascend- 
ing cerebellar  tract  (N.  9,  Add.). 

(1)  The  Fillet^^  Fibers  form  a  broad  flat  bundle  next  the 
trapezium.  The  width  of  the  bundle  is  almost  equal  to  half 
the  transverse  axis  of  the  pons;  the  lateral  fillet  lies  just 
beneath  the  dorsal  surface,  and  the  medial  runs  along  the 
raphe.     Anterior  to  the  pons  we  have  the  medial,  superior 

(25)    Lemniscus— L.   Lateralis,  L.   Medialis,  L.   Superior. 


124  THE    BRAIN    AND    SPINAL    CORD. 

and  lateral  fillets,  which  have  been  traced  through  the  teg- 
mentum of  the  mid-brain  to  the  optic  thalamus  and  the 
superior  and  inferior  quadrigeminal  bodies. 

(2)  Posterior  Longitudinal  Bundle?^ — It  is  a  small  fas- 
ciculus situated  near  the  raphe^,  and  just  beneath  the  gray 
matter  in  the  floor  of  the  fourth  ventricle.  It  is  continued 
down  into  the  anterior  column  of  the  spinal  cord  without 
decussation.  Both  ascending  and  descending  fibers  are  found 
in  it.  Its  longest  ascending  fibers  rise  in  the  anterior  cornu 
of  gray  matter  in  the  spinal  cord.  Fibers  are  added  to  it 
from  the  sensory  nuclei  of  cranial  nerves,  and  from  the 
cerebellum  by  way  of  the  middle  peduncles.  Along  its  course 
fibers  leave  it  and  end  in  the  motor  nuclei  of  cranial  nerves, 
especially  the  third  and  fourth.  The  bundle  ends  in  the 
hypothalamic  region.  Many  of  its  fibers  decussate  through 
the  raphe  in  the  medulla,  pons  and  mid-brain ;  the  remainder 
cross  through  the  posterior  commissure.  Motor  fibers  run 
through  the  posterior  longitudinal  bundle  from  the  nucleus 
of  the  sixth  to  the  third  nerve  and  from  the  motor  oculi  to 
the  facial  nerve. 

(3)  TJie  Anterior  Longitudinal  Bundle^'^  descends  from, 
the  superior  quadrigeminal  body  ventral  to  the  posterior 
longitudinal  fasciculus,  through  the  mid-brain,  pons  and 
medulla;  and,  in  the  cord,  it  runs  along  the  apex  of  the 
anterior  cornu  of  gray  matter,  in  which  it  terminates,  chiefly 
in  the  cervical  region.    It  is  the  pupillo-dilator  tract. 

(4)  The  Olivary  Bundle^^  is  an  ascending  tract.  It  be- 
gins at  the  dorsal  surface  of  the  inferior  olive,  from  which  it 
probably  rises.  It  ascends  through  the  formatio  reticularis 
of  the  medulla,  pons  and  mid-brain,  and,  according  to  Flech- 

(26)  Fasciculus   longitudinalis  medialis. 

(27)  Fasciculus  ventralls. 

(28)  Fasciculus  tegmenti  centralis. 


HIND-BRAIN.  I25 

sig,  ends  in  the  globus  pallidns  of  the  lenticular  nucleus, 
though  certain  fibers  may  continue  through  the  lenticular 
loop,  without  interruption,  to  the  cortex.  The  olivary  bundle 
is  probably  the  second  stage  in  the  afferent  tract  of  which  the 
triangiilar  tract  of  Helwig  is  the  first  stage.  In  the  posterior 
part  of  the  pons,  the  olivary  bundle  lies  on  the  lateral  part  of 
the  trapezium,  between  it  and  the  fillet.  Higher  up  it  is  in 
the  center  of  the  formatio  reticularis,  hence  its  synonym, 
central  tegmental  tract. 

(5)  Crossed  Descending  Tract  of  the  Red  Nucleus. — It  is 
found  in  the  pons  among  the  medial  fibers  of  the  lateral 
fillet.  It  runs  from  the  red  nucleus  through  the  raphe,  in 
the  upper  part  of  the  mid-brain;  and,  from  there,  descends 
to  the  lumbar  region  of  the  spinal  cord  (Barker).  Its  fibers 
gradually  disappear  in  the  lateral  horn  and  center  of  the 
crescent  of  gray  matter  (see  Mid-Brain,  p.  65). 

(6)  Ascending  Boot  of  the  Trifacial  or  Fifth  Nerve  (in- 
ferior sensory  root)  .^^ — ^In  the  lower  half  of  the  pons  is  seen 
a  small  bundle  of  fibers  which  begins  near  the  tubercle  of 
Eolando  in  the  medulla  oblongata.  It  runs  forward  close  to 
the  lateral  part  of  the  floor  of  the  fourth  ventricle  and  joins 
the  superior  sensory  root  ventral  to  the  superior  cerebellar 
peduncle. 

The  Dorsal  Longitudinal  Fibers  (superficial  longitudinal) 
form  the  medial  portion  of  the  dorsal  surface  of  the  pons. 
They  bound  laterally  and  form  the  roof  of  the  superior  half 
of  the  fourth  ventricle.  The  dorsal  longitudinal  fibers  com- 
pose the  superior  peduncles  of  the  cerebellum  and  the  valve 
of  Vieussens.  The  peduncles  rest  on  the  formatio  reticu- 
laris. Between  them  the  valve  arches  over  the  fourth  ven- 
tricle  (see  Cerebellum,  pages  102,  114). 

(29)    Tractus  spinalis  nervi  trigemini. 


126  THE    BRAIN    AND   SPINAL    CORD. 

GRAY    MATTER   OF   THE   PONS. 

In  the  pons  gray  matter  is  found  in  two  situations:  (1) 
In  the  interstices  between  the  middle  transverse  and  ventral 
longitudinal  fibers,  the  nuclei  pontis;  and  (2)  in  the  for- 
matio  reticularis,  the  floor  of  the  fourth  ventricle. 

The  nuclei  pontis  are  masses  of  gray  matter,  on  either  side 
the  raphe,  containing  the  bodies  of  multipolar  nerve  cells. 
They  receive  many  fibers  from  the  middle  peduncles  of  the 
cerebellum  and  each  contributes  many  to  the  opposite  pe- 
duncle. The  nucleus  pontis  of  each  side  receives  the  ter- 
minals of  the  descending  tracts  which  form  the  inner  and 
outer  fifths  of  the  crusta  and  the  intermediate  bundle  of  the 
same,  and  thus  connects  these  tracts  with  the  cerebellum. 

The  gray  matter  of  the  formatio  reticularis  includes  the 
fc^uperior  olive;  the  nuclei  of  the  trapezium;  the  nuclei  of 
the  formatio  reticularis;  and  the  nuclei  of  the  fifth,  sixth 
and  seventh  cranial  nerves,  and  a  part  of  the  dorsal  nucleus 
of  the  auditory  nerve.  The  nerve  nuclei  will  be  further 
noticed  in  the  description  of  the  fourth  ventricle. 

Superior  Olivary  Nucleus. ^^ — It  is  situated  in  the  lateral 
part  of  the  formatio  reticularis  in  the  dorsal  portion  of  the 
trapezium.  It  contains  small  bodied  nerve  cells;  and,  in 
this  respect,  resembles  the  oKve  of  the  medulla.  In  size  it 
is  microscopic.  The  superior  olive  constitutes  a  subordinate 
relay  in  the  auditory  path,  receiving  fibers  from  the  cochlear 
nuclei  of  both  sides  and  contributing  fibers  to  both  lateral 
fille^riS,  In  their  course  to  the  fillets,  fibers  of  the  auditory 
path  form  the  trapezium  (N.  10,  Add.). 

Nuclei  of  the  Formatio  Reticularis. — These  nuclei  are 
scattered  in  the  reticular  formation  from  the  medulla  to  the 
superio  quadrigeminal  bodies.     They  contain  the  bodies  of 

(30)    Nucleus  olivaris  superior. 


HIND-BRAIN.  I27 

large  multipolar  cells,  hence  the  name  adopted  by  Koelliker, 
Nucleus  magnocellularis  diffusus.  The  nuclei  are  interposed 
in  the  frequently  interrupted  tracts  of  the  reticular  forma- 
tion. Their  neurones,  which  are  both  ascending  and  de- 
scending in  conduction,  send  their  axones  toward  the  raphe, 
where  they  cross  to  the  opposite  side.  Axones  of  Purkinje's 
cells  and  collaterals  from  the  nuclei  of  cranial  nerves  ter- 
minate in  relation  with  them. 

Lesions  in  the  pons  are  usually  attended  by  crossed  paraly- 
sis. The  paralysis  and  anesthesia  of  parts  supplied  by  spinal 
and  by  bulbar  cranial  nerves  are  on  the  opposite  side,  but 
the  fifth,  sixth  and  seventh  cranial  nerves  of  the  same  side 
as  the  lesion  are  apt  to  be  involved.  Conjugate  deviation 
occurs  when  the  nucleus  of  the  sixth  nerve  is  affected;  and 
strabismus  when  the  root  fibers,  but  not  the  nucleus,  are 
involved.  The  strabismus  is  external  if  the  lesion  be  irrita- 
tive and  internal  if  the  root  fibers  are  destroyed.  Destructive 
lesion  in  the  nucleus  of  the  seventh  nerve  causes  inferior 
paralysis  of  the  face,  the  frontalis,  pjrramidalis  nasi,  corru- 
gator  supercilii  and  orbicularis  palpebrarum  not  being 
affected.  Complete  facial  paralysis  occurs  if  the  root-fibers 
of  the  facial  nerve  be  destroyed  in  the  genu  or  beyond  it. 

BLOOD    SUPPLY    OF    PONS. 

The  vertebral,  basilar,  posterior  cerebral  and  superior  cere- 
bellar arteries  supply  the  pons.  The  short  and  transverse 
branches  of  the  basilar  artery  furnish  the  greater  portion  of 
blood  to  the  ventral  area  of  the  pons,  while  the  superior 
cerebellar  artery  supplies  the  valve  of  Yieussens^^  and  the 
superior  cerebellar  peduncles.^^  The  branches  enter  the 
median  raphe,  also  the  substance  of  the  pons  elsewhere,  es- 
pecially along  the  nerve  roots,  and  run  at  right  angles  to  the 
surface  into  it. 

(31)  Velum  medullare  anterius. 

(32)  Brachia  conjunctiva. 


CHAPTER  VI. 


THE    AFTER-BRAIN,    OR    MEDULLA    OBLONGATA. 

Situation. — The  medulla  oblongata  is  the  distal,  or  caudal, 
part  of  the  brain.  It  may  be  regarded  as  the  expanded  intra- 
cranial portion  of  the  spinal  cord,  hence  the  synonym,  spinal 
huTb.  It  occupies  the  basilar  groove  of  the  occipital  bone, 
posterior  to  the  pons;  and  is  continuous  with  the  spinal  cord 
through  the  foramen  magnum.  Dorsally,  it  is  in  part  con- 
cealed in  the  valley  of  the  cerebellum.  The  vertebral  arteries 
wind  forward  around  it,  and  form  the  basilar  at  its  junction 
with  the  pons. 

Size. — The  medulla  is  about  an  inch  long,  and  dorso- 
ventrally,  is  a  half-inch  thick.  Its  width  at  the  lower  end  is 
a  half-inch,  also.  At  the  upper  extremity  it  measures  from 
three-quarters  of  an  inch  to  one  inch  in  width. 

Its  shape  resembles  an  inverted  frustum  of  a  cone  flattened 
dorso-ventrally  at  the  base.  The  truncated  apex  of  the 
frustum,  which  is  nearly  circular  in  outline,  is  continuous 
with  the  spinal  cord;  and  the  flattened  base  joins  the  pons 
Varolii.  On  the  ventral  surface,  a  transverse  groove  marks 
the  boundary  between  the  medulla  and  pons.  The  medulla 
oblongata  is  a  bilateral  organ  composed  of  symmetrical 
halves.  In  the  interior,  the  two  halves  are  united  by  both 
gray  and  white  matter  in  the  raphe,  but  on  the  surface  they 
are  partially  separated  by  the  anterior  and  the  posterior 
median  fissure.^    These  fissures  are  continuations  of  the  same 

(1)    Fissura  mediana  anterior,  posterior. 


THE    AFTER-BRAIN.  I29 

in  the  spinal  cord,  but  neither  extends  the  whole  length  of 
the  medulla.  The  anterior  median  fissure  is  interrupted 
in  the  lower  part  of  the  medulla  by  the  crossing  of  two  large 
tracts  of  fibers,  forming  the  decussation  of  the  pyramids; 
while  only  through  the  lower  half  of  the  medulla  does  the 
posterior  median  fissure  extend. 

Origin. — The  medulla  oblongata  is  developed  from  the 
metencephalon  (myelencephalon)  of  the  embryo.  The  met- 
encephalic  floor  and  walls  thicken  and  form  the  greater  part 
of  the  medulla.  Infer iorly,  the  roof  undergoes  some  thick- 
ening; but  it  stretches  out  into  a  single  layer  of  epithelium, 
superiorly,  which  is  continuous  at  its  upper  end  with  the 
inferior  medullary  velum  of  the  cerebellum. 

Ventricle. — The  common  cavity  of  the  fourth  and  fifth 
brain  vesicles  persists  in  the  mature  brain  as  the  fourth  ven- 
tricle. The  fourth  is,  therefore,  the  ventricle  of  the  adult 
hind-brain  and  after-brain. 

SURFACES. 

The  Medulla  Oblongata  presents  four  surfaces:  The  ven- 
tral, dorsal  and  two  lateral,  separated  by  the  vehtro-lateral 
and  dorso-lateral  grooves.  In  the  upper  medulla,  the  sur- 
faces are  clearly  defined;  but  they  become  less  distinct  as 
they  descend  to  the  posterior  and  nearly  circular  extremity. 

The  Y entro-lateral  Groove^  separates  the  ventral  from  the 
lateral  surface,  and  is  in  line  with  the  exits  of  the  anterior 
roots  of  the  spinal  nerves.  No  corresponding  groove  exists 
in  the  cord.  From  the  ventro-lateral  groove  issue  the  roots 
of  the  hypoglossal  nerve.  The  abducent  (or  sixth)  nerve 
rises  in  line  with  it  from  the  transverse  groove  between  the 
pons  and  the  medulla. 

Dorso-lateral   Groove. — The  posterolateral  fissure  of  the 

(2)    Sulcus  lateralis  anterior. 


130  THE    BRAIN    AND    SPINAL    CORD. 

spinal  cord,  continued  into  the  medulla,  becomes  the  dorso- 
lateral groove.^  Through  the  fissure  in  the  cord,  pass  the 
posterior  roots  of  the  spinal  nerves;  from  the  groove  in  the 
medulla,  rise  the  accessoiy  root  of  the  eleventh  and  the  roots 
of  the  tenth  and  ninth  cranial  nerves.  The  seventh  and 
eighth  cranial  nerves  rise  together  at  the  anterior  end  of  the 
groove.  The  last  two  come  out  between  the  medulla  and 
pons.  The  dorso-lateral  groove  is  not  parallel  with  the  axis 
of  the  medulla,  but  bends  outward  and  forward  as  it  ascends. 
Inferiorly,  it  is  obliterated  for  a  short  distance  by  the  crossing 
of  the  direct  cerebellar  tract  from  the  lateral  to  the  posterior 
surface.  This  groove  separates  the  lateral  from  the  dorsal 
surface. 

The  Ventral  Surface*  of  the  medulla,  bounded  on  either 
side  by  the  ventro-lateral  groove,  extends  from  the  transverse 
sulcus  behind  the  pons  down  to  the  spinal  cord.  It  is  made 
up  of  symmetrical  halves  united,  below,  by  the  decussation  of 
the  crossed  pyramidal  tracts;  but  separated,  above,  by  the 
anterior  median  fissure,  which  terminates  at  the  posterior 
end  of  the  pons  in  a  blind  foramen  (foramen  caecum  of  Vicq 
d'Azyr).  On  either  side  of  the  median  fissure,  the  ventral 
surface  presents  a  fusiform  eminence,  most  prominent  near 
the  pons,  called  the  pyramid.  Two  tracts  of  longitudinal 
fibers  form  the  pyramid,  viz. :  The  crossed  pyramidal  tract, 
next  the  anterior  median  fissure;  and  the  uncrossed  (direct) 
pyramidal  tract,  which  runs  next  the  ventro-lateral  groove. 
Transverse  fibers  are  also  seen  crossing  the  pyramid  from 
within  outwaj-d.  A  small  bundle  runs  near^the  pons,  called 
the  ponticulus  of  Arnold;  and  a  more  or  less  continuous 
sheet  of  fibers,  the  anterior  external  arciform  fibers,  emerges 
from  the  anterior  median  fissure  and  winds  around  the  me- 

(3)    Sulcus    lateralis    posterior.  (4)    Facies  anterior. 


THE    AFTER-BRAIN.  I3I 

dulla  to  the  dorsal  surface,  where  its  fibers  enter  the  restiform 
body. 

The  ventral  surface  is  identical  with  the  surface  of  the  two 
anterior  areas  of  the  medulla. 

Lateral  Surface. — There  are  a  right  and  a  left  lateral 
surface.^  Each  is  bounded  by  the  ventrolateral  and  the 
dorso-lateral  grooves;  and  is  inclosed  between  the  roots  of 
the  hypoglossal  nerve,  ventrally,  and  those  of  the  ninth,  tenth 
and  the  accessory  portion  of  the  eleventh,  dorsally.  Lateral 
surface  is  synonymous  with  surface  of  the  lateral  area.  The 
lateral  surface  is  formed  above  by  the  olivary  hody,^  below, 
by  the  lateral  tract;  and  winding  backward  over  both,  the 
anterior  external  arciform  fibers. 

The  Olivary  Body  is  an  elongated  eminence,  a  half-inch  in 
length,  situated  just  behind  the  pons.  It  is  produced  by  the 
olivary  nucleus  in  the  lateral  area  of  the  medulla;  and, 
superficially,  is  composed  of  fibers  from  the  antero-lateral 
ground  bundle  of  the  lateral  tract. 

Lateral  Tract? — It  is  made  up  of  three  great  bundles  of 
fibers :  The  antero-latei'al  ground  bundle,^  which,  splitting 
into  a  superficial  and  a  deep  lamina,  incloses  the  olivary 
nucleus;  the  antero-lateral  descending  cerebellar  tract,^  run- 
ning down  the  ventro-lateral  groove;  and  the  antero-lateral 
ascending  cerebellar  tract p  which  runs  up  the  dorso-lateral 
groove.  At  the  junction  of  the  medulla  with  the  spinal  cord 
the  direct  cerebellar  tract  passes  from  the  lateral  to  the  dorsal 
surface.  The  anterior  external  arciform  fibers}^  running 
from  the  ventral  surface  backward  to  the  restiform  body,  may 

(5)  Fades   lateralis. 

(6)  Oliva. 

(7)  Funiculus   lateralis. 

(8)  Fasciculus  proprius  antero-lateralis. 

(9)  Fasciculus  antero-lateralis  superficialis  (descendens  and  as- 
cendens). 

(10)  Fibrse  arcuatse  extemse. 


132  THE    BRAIN   AND   SPINAL    CORD. 

be  SO  numerous  as  to  conceal  the  lateral  tract  and  lower  part, 
of  the  olive.  ' 

The  Dorsal  Surface  of  the  medulla^^  comprises  all  the  sur- 
face inclosed  between  the  diverg-ing  dorso-lateral  grooves.  It 
embraces  the  surfaces  of  the  two  posterior  areas  of  the 
medulla. 

Inferiorly,  it  is  divided  into  lateral  halves  by  the  posterior 
median  fissure/ ^  an^d  presents  four  bundles  of  fibers  in  each 
half.  From  the  fissure  outward  they  are  as  follows:  The 
fasciculus  gracilis,  fasciculus  cuneatus,  fasciculus  of  Eolando, 
and  the  direct  cerebellar  tract. 

The  fasciculus  gracilis  is  a  continuation  of  the  postero- 
median column  of  the  spinal  cord,  and  the  fasciculus  cunsor 
tus  and  fasciculus  of  Rolando  are  in  direct  continuity  with 
the  postero-Iateral  column  of  the  cord.  These  three  bundles 
leave  the  surface  and  end  in  the  gracile,  cuneate  and  Rolandic 
nuclei  of  the  medulla.  The  direct  cerebellar  tract  is  con- 
tinued up  from  the  lateral  column  of  the  spinal  cord.  Ke- 
maining  on  the  surface,  it  runs  up  to  the  cerebellum  through 
the  restiform  body. 

Superiorly,  the  dorsal  surface,  on  either  side,  is  formed 
by  a  large  rounded  band  of  fibers,  the  restiform  hody}^  Of 
the  superficial  fibers  in  the  medulla,  the  direct  cerebellar 
tract,  the  antero-lateral  descending  cerebellar  tract  and  the 
anterior  and  posterior  external  arciform  fibers  are  con- 
tinued into  the  restiform  body;  and,  as  we  have  already 
learned,  the  restiform  body  contains,  in  addition  to  the  above 
three  tracts,  the  acustico-cerebellar  tract,  the  tract  from  the 
lateral  nucleus  and  the  cerebello-olivary  tract.  It  is  also 
called  the  inferior  peduncle  of  the  cerebellum.  A  single 
layer  of  flattened  epithelial  cells  stretches  between  the  two 
restiform  bodies,  and  roofs  over  the  posterior  part  of  the 

(11)  Facies  posterior.  (13)    Corpus  restiforme. 

(12)  Fissura  mediana  posterior. 


THE   AFTER-BRAIN.  I33 

fourth  ventricle.    It  is  the  roof  epithelium.    By  it  the  dorsal 
surface  is  completed. 

The  Roof  Epithelium,  seen  in  the  mid-dorsal  surface  of 
the  medulla,  is  of  triangular  shape;  its  base  is  attached  to  the 
inferior  medullary  velum  of  the  cerebellum;  its  apex,  which 
is  directed  downward,  covers  the  inferior  angle  of  the  fourth 
ventricle;  and,  laterally,  it  is  attached  to  the  clava,  the. 
cuneate  tubercle  and  the  restiform  body.  The  line  of  at- 
tachment to  the  restiform  body  runs,  first,  obliquely  upward 
and  outward;  and  then,  transversely  outward,  inferior  to  the 
lateral  recess.  The  borders  of  the  epithelium  become  thick- 
ened by  the  addition  of  neuroglia,  and  are  in  continuity  with, 
the  ependyma  of  the  ventricle.  The  thickened  apex  of  the 
epithelial  lamina  is  called  the  obex.  With  the  pia  mater 
investing •  it,  termed  the  inferior  choroid  tela}'^  this  roof 
epitheliuni  is  perforated  in  the  median  line  near  its  apex 
by  a  foramen,  the  foramen  of  Magendie,^^  and  over  each 
kteral  recess  by  the  foramen  of  Key  and  Eetzius.^^  These 
foramina  establish  communication  between  the  subarach- 
noid space  and  the  ventricle.  On  either  side  of  the  median 
line,  a  longitudinal  invagination  of  the  epithelial  lamina 
dips  into  the  ventricle  and  is  occupied  by  a  vascular  fold  of 
pia  mater.  The  latter  constitutes  the  choroid  plexus^'^  of  the 
fourth  ventricle.  If  the  roof  epithelium  be  torn  away,  as  it 
usually  is  with  the  pia,  a  rough  line  of  separation  is  seen 
winding  over  the  restiform  body.  That  line  is  the  ligula. 
Two  layers  of  ependyma  form  it. 

-^^^T"  WHITE   MATTER   OF   MEDULLA. 

The  medulla  is  made  up  of  white  and  gray  matter,  which 
together  bound  ventrally  and  laterally  the  inferior  part  of 

(14)  Tela   choroidea  ventriculi   quarti. 

(15)  Apertura  mediana  ventriculi  quarti. 

(16)  Aperturse  laterales  ventriculi  quarti. 

(17)  Plexus  choraid^us  ventriculi  quarti. 


134  THE    BRAIN    AND   SPINAL    CORD. 

the  fourth  ventricle  and  surround  the  upper  extremity  of  the 
sixth  ventricle. 

For  the  most  part  the  white  matter  of  the  medulla  is  con- 
tinuous with  the  longitudinal  fibers  of  the  pons  and  spinal 
cord,  above  and  below,  respectively ;  and  with  the  inferior 
peduncles  of  the  cerebellum,  dorso-laterally.  To  these  add 
the  bulbar  roots  of  the  eighth  to  the  twelfth  cranial  nerves 
to  complete  the  list. 

Formatio  Reticularis. — Superficially,  the  white  matter  is 
collected  into  great  bundles  of  fibers,  such  as  the  pyramids, 
lateral  tracts  and  restiform  body;  but,  in  the  deep  parts  of 
the  medulla,  the  white  matter  enters  into  a  great  network 
called  the  formatio  reticularis,  which  has  gray  matter  in  its 
meshes  and  embraces  all  the  medulla  between  the  ventricular 
gray  matter,  dor  sally,  and  the  pyramid,  olivary  nucleus,  and 
restiform  body,  ventro-laterally.  The  formatio  reticularis 
contains  many  scattered  fibers,  processes  of  its  intrinsic  neu- 
rones, which  form  a  frequently  interrupted  and,  for  the  most 
part,  a  crossed  ascending  and  descending  tract.  It  is  con- 
tinuous, above,  with  the  reticular  formation  of  the  pons,  and, 
below,  with  the  ground  bundles  of  the  spinal  cord.  It  con- 
tains several  distinct  fasciculi  of  longitudinal  fibers  of  which 
the  following  are  the  best  understood :  The  posterior  and  an- 
terior longitudinal  bundles  and  the  descending  crossed  tract 
of  the  red  nucleus,  which  run  throughout  the  medulla  and 
are  continued  in  the  cord;  and,  in  the  upper  part  of  the 
medulla,  the  interolivary  fillet  (medial  and  superior),  the 
olivary  bundle  and  the  inferior,  or  spinal,  root  of  the  fifth 
cranial  nerve.  Transverse  and  oblique  fibers  are,  likewise, 
numerous  in  the  reticular  formation.  They  are  the  internal 
arciform  fibers.  In  the  formatio  reticularis  is  much  gray 
matter  which  may  be  considered  as  the  disintegrated  H- 
shaped  column  continued  up  from  the  spinal  cord. 


THE    AFTER-BRAIN.  135 

Raphe. — Fibers  form  only  a  part  of  the  raphe  which  unites 
the  lateral  halves  of  the  medulla.  The  raphe  is,  primarily, 
a  sagittal  lamina  of  neuroglia  containing  the  bodies  of  nerve- 
cells  and  decussating,  dorso- ventral  and  longitudinal  fibers: 
(a)  The  decussating  fibers  are  chiefly  the  internal  arciform. 
A  few  are  commissural  fibers  between  the  nuclei  of  the  pos- 
terior five  cranial  nerves,  (b)  Issuing  from  the  anterior 
median  fissure,  the  dorso-ventral  fibers  become  the  anterior 
external  arciform  fibers.  Traced  dorsally,  some  of  them  are 
found  continuous  with  the  acustic  striae  in  the  floor  of  the 
fourth  ventricle,  while  the  greater  number  rise  from  the 
opposite  nuclei  gracilis  et  cuneatiis.  (c)  The  origin  and 
destination  of  the  longitudinal  fibers  are  unknown. 

The  white  matter  of  the  medulla  is  divided  by  the  direction 
of  its  fibers  into  three  classes  or  systems :  ( 1 )  Transverse 
fibers;  (2)  Dorso-ventral  fibers;  and  (3)  Longitudinal 
fibers. 

(1)  The  Transverse  Fibers  of  the  medulla  are  chiefly  the 
external  and  internal  arciform  fibers.^^  The  anterior  exter- 
fial  arciform  fihers^^  rise  in  the  nucleus  gracilis  and  nucleus 
cuneatus  of  the  opposite  side,  decussate  in  the  raphe  and  issue 
from  the  anterior  median  fissure  and  ventral  surface  of  the 
medulla,  whence  they  have  been  traced  over  the  surface  to 
the  restiform  body.  Perhaps  a  few  are  interrupted  in  the 
external  arciform  nucleus.  The  posterior  external  arciform 
fihers^^  rise  from  the  same  nuclei  and  enter  the  cerebellum, 
through  the  inferior  peduncle,  without  decussation.  Both 
groups  of  fibers  end  in  the  cortex  of  the  vermis  cerebelli 
superior.  The  internal  arciform  fibers  are  contained  in  the 
formatio  reticularis.    They  are  disposed  in  two  groups,  viz. : 


(18)  Flbrse  arcuatse. 

(19)  Fibrse  arcuatse  externa  anterior,  posterior. 


136  THE    BRAIN    AND    SPINAL    CORD. 

Those  of  the  sensory  decussation,  and  those  of  the  olivary 
peduncle. 

The  fibers  of  the  Setisory  Decussation^^  rise  chiefly  from 
the  nucleus  gracilis  and  nucleus  cuneatus.  Bending  ven- 
trally  through  the  posterior  horn  of  gray  matter,  they  decus- 
sate through  the  median  raphe;  and,  then,  the  greater  num- 
lier  run  forward  toward  the  cerebrum  as  the  interolivary 
fillet  (medial  and  superior  fillets) ;  the  remainder  constitute 
the  deep  part  of  the  anterior  external  arcifornp  fibers.  The 
sensory,  or  fillet,  decussation  is  nearer  the  pons  and  dorsal 
to  the  decussation  of  the  pyrami'ds. 

The  Olivary  Peduncle  is  a  sheet  of  fibers  extending  between 
the  two  olivary  nuclei  of  the  medulla.  It  is  the  inferior  por- 
tion of  the  cerehello-olivary  tract?^  It  is  composed  of  axones 
from  Purkinje's  cells.  Descending  to  the  medulla  through 
the  inferior  cerebellar  peduncle,  it  pierces  the  olive,  crosses 
through  the  raphe  and  terminates  in  the  olivary  body  of  the 
opposite  side.  The  cerebello-olivary  tract  connects  the  cere- 
bellar hemisphere  with  the  opposite  nucleus. 

(2)  The  Dorso- ventral  Fibers  of  the  medulla  are  found 
in  three  situations:  (a)  In  the  raphe,  (b)  between  the  ante- 
rior and  lateral  areas,  and  (c)  between  the  lateral  and  poste- 
rior areas. 

(a)  The  dorso-ventral  fibers  of  the  raphe  are  the  ante- 
rior external  arciform  fibers.  These  can  be  traced  to  the  cere- 
bellum through  the  restiform  body.  Their  origin  is  chiefly 
in  the  nuclei  gracilis  et  cuneatus.  Some  of  them  seem  to  be 
interrupted  in  the  arciform  nuclei  on  the  ventral  surface  of 
the  pyramids.  The  root-bundles  of  the  eighth  to  the  twelfth 
cranial  nerves  constitute  the  remaining  groups  of  dorso- 
ventral  fibers.    By  them  the  medulla  is  divided  into  areas. 

(20)    Decussatio  lemniscorum.  (20    Fibrse  cerebello-olivares. 


THE    AFTER-BRAIN.  137 

(b)  The  root-bundles  of  the  hypoglossal  nerve^^  run  from 
the  ventricular  gray  matter,  near  the  median  line,  ventro- 
laterally  to  the  ventro-lateral  groove,  where  they  emerge.  In- 
closing between  them  and  the  raphe,  the  anterior  area,  they 
also  separate  it  from  the  lateral  area.  The  anterior  and 
lateral  areas  are  bounded  dorsally  by  the  thick  sheet  of  gray 
matter  in  the  floor  of  the  fourth  ventricle. 

(c)  The  medial  root^^  of  the  auditory  nerve,  the  roots  of 
gJosso-pharyngeal^^  and  vagv^^^  and  the  accessory  root  of  the 
eleventh^^  form  the  third  .group  of  dorso-ventral  fibers. 
From  the  dorso-lateral  groove,  which  is  their  superficial 
origin,  they  may  be  traced  through  the  medulla  to  ventricular 
gray  matter  external  to  the  column  of  cells  from  which  the 
twelfth  nerve  rises.  Tbey  separate  the  lateral  from  the  poste- 
rior area.  The  posterior  area  comprises  everything  dorsal  to 
the  above  roots  of  the  eighth  to  eleventh  cranial  nerves.  It 
thus  includes  the  gray  matter  in  the  floor  of  the  fourth  ven- 
tricle. 

(3)  longitudinal  Fibers. — In  the  medulla,  the  longitu- 
dinal fibers  are  chiefly  continuations  of  the  same  in  the  spinal 
cord.  They  can  be  best  located  by  reference  to  the  three 
areas  bounded  by  the  above  dorso-ventral  fibers,  namely.  An- 
terior, Lateral  and  Posterior  areas. 

ANTERIOR   AREA. 

The  anterior  area  of  the  medulla  lies  between  the  raphe 
and  the  roots  of  the  hypoglossal  nerve,  and  between  the 
ventral  surface  and  the  gray  matter  in  the  floor  of  the  fourth 
ventricle.  Excepting  that  part  forming  the  crossed  pyram- 
idal tract  and  the  interolivary  fillet,  it  is  continued  in  the 

(22)  Nervus  hypoglossus. 

(23)  Radix  nervi  vestibularis. 

(24)  Radix  nervi  glossopharyngei. 

(25)  Radix  nervi  vagi. 

(26)  Radix  cerebralis  nervi  accessorii. 


138  THE    BRAIN    AND    SPINAL    CORD. 

anterior  column  of  the  spinal  cord.  It  is  naturally  divided 
into  a  ventral  and  a  dorsal  part,  or  the  region  of  the  pyra- 
niid27  and  the  region  of  the  formatio  reticularis  alba. 

The  Pyramid,  with  the  arciform  nucleus  imbedded  in  it, 
and  the  arciform  fibers  winding  over  it,  occupies  the  ventral 
portion  of  the  anterior  area.  It  is  the  continuation  of  the 
pyramidal  tract  and  is  composed  of  the  axones  of  cortical 
cells  in  the  Rolandic  region  of  the  cerebrum.  The  pyram- 
idal tract  diminishes  in  size  as  it  descends  through  the  pons 
and  medulla,  because  some  of  its  fibers  terminate  in  ramifica- 
tions about  the  cells  of  cranial  nerve-nuclei.  In  the  lower 
part  of  the  medulla,  the  pyramid  breaks  up  into  the  un- 
crossed (direct)  pyramidal  tracP^  (10  to  20  per  cent  of  the 
pyramid),  which  descends  along  the  anterior  median  fissure 
in  the  same  side  of  the  spinal  cord;  and  the  crossed  pyram- 
idal tract^^  (80  to  90  per  cent  of  the  pyramid),  which,  after 
decussating  with  its  fellow  through  the  anterior  median 
fissure,  runs  down  in  the  lateral  column  of  the  opposite  side 
of  the  cord.  The  fibers  of  the  direct  tract  cross  in  succession 
to  the  opposite  side  of  the  cord,  through  the  anterior,  or 
white,  commissure;  and  there,  with  the  fibers  of  the  crossed 
pyramidal  tract,  terminate  in  fibrillar  end-tufts  about  the 
cell-bodies  in  the  anterior  comu  of  gray  matter.  Thus  the 
pyramid  forms  a  crossed  cerebral  tract  for  efferent  (motor)~ 
cranial  and  spinal  nerves.  A  small  number  of  pyramidal 
fibers  (20  per  cent,  Marchi)  descend  in  the  lateral  column 
of  the  cord  without  decussation.  They  account  for  the  weak- 
ness on  the  well  side,  and  for  slight  motion  on  the  paralyzed 
side,  which  are  commonly  observed  in  hemiplegia.  (N.  15, 
Add.) 

(27)  Pyramis  meduUfe  oblongatae. 

(28)  Fasciculus  cerebro-spinalis   anterior   (ventralis). 
^29)    Fasciculus   cerebro-spinalis  lateralis, 


THE    AFTER-BRAIN.  139 

The  dorsal  part  of  the  anterior  area  is  occupied  by  the 
formatio  reticularis  alha.  Gray  matter  from  the  anterior 
horn  is  sparsely  scattered  throughout  the  reticular  formation, 
but  it  contains  the  bodies  of  very  few  nerve  cells  and  is  of  a 
light  color.  The  intei^nal  accessory  olivary  nucleus  is  im- 
bedded in  it  near  the  pyramid  and  among  the  fibers  of  the 
fillet;  and  three  definite  bundles  of  longitudinal  fibers  have 
been  demonstrated  in  it,  namely,  the  Interolivary  Fillet,  the 
Posterior  and  the  Anterior  longitudinal  bundles. 

Interolivary  Fillet. — ^Just  dorsal  to  the  pyramid  in  the 
anterior  area  of  the  medulla,  is  a  large  bundle  of  fibers  called 
the  interolivary  fillet.^^  Situated  between  the  inferior  oli- 
vary bodies,  it  is  on  that  account  called  the  interolivary  fillet. 
Superiorly,  it  is  continued  in  the  medial  and  superior 
fillets.^'^  The  interolivary  fillet  rises  from  the  nucleus  gracilis 
and  nucleus  cuneatus  of  the  medulla  and  crosses  through  the 
median  raphe  in  the  sensory  decussation.  As  the  fillet  runs 
brain  ward  through  the  reticular  formation  of  the  pons  and 
mid-brain,  it  receives  fibers  from  the  terminal  nuclei  of 
sensory  cranial  nerves,  except  the  cochlear  nuclei,  and  from 
the  middle  peduncles  of  the  cerebellum.  Externally,  it  is 
accompanied  for  a  short  distance  in  the  pons  by  the  lateral 
fillet.^2  The  interolivary  fillet  is  composed  of  ascending 
axones  which  constitute  a  "cerebral"  tract  for  the  afferent,  or 
sensory,  fibers  of  spinal  and  cranial  nerves.  It  carries  ordi- 
nary sensations  to  the  superior  quadrigeminal  body  by  the 
superior  fillet,  and  to  the  optic  thalamus  by  the  medial  fillet. 

The  Posterior  Longitudinal  Bundle^^  is  a  small  fasciculus 
composed  of  fibers  continued  up  from  the  anterior  column  of 

(30)  Lemniscus  interolivarls. 

(31)  Lemniscus   medialis   et   lemniscus   supertar. 

(32)  Lemniscus  lateralis. 

(33)  Fasciculus  longitudinalis  medialis. 


140  THE    BRAIN    AND   SPINAL    CORD. 

the  spinal  cord.  Its  origin  is  in  the  anterior  horn  of  gray 
matter.  In  the  medulla  it  runs  along  the  median  raphe  in 
contact  with  the  ventricular  gray  matter,  and  is  augmented 
in  the  medulla  and  pons  by  fibers  from  the  terminal  nuclei 
of  the  sensory  cranial  nerves  and  by  fibers  from  the  nuclei  of 
the  abducent  nerves  and  the  middle  cerebellar  peduncle. 
Further  forward,  some  of  these  fibers  and  others  of  spinal 
origin  leave  the  bundle  to  end,  chiefly  on  the  opposite  side,  in 
the  motor  cranial  nerve-nuclei,  especially  the  third.  Fibers 
join  the  posterior  longitudinal  bundle  in  the  mid-brain  from 
the  motor  oculi  nucleus,  and  descend  to  the  genu  of  the 
facial  nerve.  The  posterior  longitudinal  bundle  ends,  supe- 
riorly, in  the  thalamus  or  hypothalamus.  It  associates  spinal 
and  cranial  nerves  with  one  another,  forming  part  of  a  reflex 
arc.  It  also  connects  the  cerebellum  with  opposite  cranial 
nuclei  and  probably  conducts  ordinary  sensation  to  the 
thalamus  (see  Mid-Brain). 

Anterior  Longitudinal  Bundle.  —  The  pupillo-dilator 
tract^*  rises  from  the  superior  quadrigeminal  body,  and  is 
seen  just  ventral  to  the  posterior  longitudinal  bundle,  which 
it  accompanies  all  the  way  down  to  its  chief  termination  in 
the  ciliospinal  centers  of  the  cervical  cord  (see  Mid-Brain). 

LATERAL  AKEA. 

Contents:  Superficially,  the  antero-lateral  ground  bundle 
and  antero-lateral  descending  and  ascending  cerebellar  tracts; 
Deeply,  the  formatio  reticularis  grisea.  Imbedded  in  the 
formatio  reticularis  are  the  nucleus  ambiguus,  the  lateral 
nucleus,  the  olivary  nucleus  and  external  accessory  olivary 
nucleus. 

The  gray  matter  of  the  formatio  reticularis  grisea  is  a 

(34)    Fasciculus  longltudinalis  ventralls. 


THE   AFTER-BRAIN.  I4I 

part  of  the  disintegrated  anterior  gray  horn  and,  unlike  that 
of  the  anterior  area,  it  contains  the  bodies  of  many  large 
nerve  cells. 

Antero-lateral  Ground  Bundle.^^ — The  whole  lateral  col- 
umn of  the  spinal  cord,  except  the  crossed  pyramidal  and 
direct  cerebellar  tracts,  is  continued  into  the  lateral  area  of 
the  medulla.  Composed  of  ascending  and  descending  axones 
which  are  commissural  and  associative  for  different  segments 
of  the  spinal  cord,  the  lateral  ground  bundle  ascends  into 
the  medulla,  and  runs  in  part  beneath  and  in  part  superficial 
to  the  olivary  nucleus;  beyond  the  olive,  it  is  continued  in 
the  formatio  reticularis  grisea  of  the  medulla  and  reticular 
formation  of  pons  and  mid-brain.  Among  the  fibers  of  the 
antero-lateral  ground  bundle,  ventral  to  the  olive,  is  the 
tnangular  tract^^  of  Helwig  and,  dorsal  to  the  olive,  the 
olivary  bundle.  The  former  is  believed  to  end  in  the  olive  of 
the  medulla  and  the  latter  to  rise  from  it.  They  are  made 
up  of  ascending  axones  and,  according  to  Bechterew,  form  a 
functionally  continuous  tract. 

The  Antero-lateral  Descending  Cerebellar  Tract^'^  rises  in 
the  cerebellar  cortex.  It  forms  part  of  the  inferior  peduncle 
of  the  cerebellum,  through  which  it  reaches  the  medulla.  In 
the  lateral  area,  it  descends  along  the  ventro-lateral  groove, 
bet\^een  the  lateral  tract  and  pyramid,  to  the  corresponding 
area  of  the  cord.  It  ends  in  the  anterior  cornu  of  gray 
matter.  Fibers  from  the  cerebral  cortex  are  scattered 
through  the  bundle  in  the  cord,  and  it  was  once  regarded  as ' 
a  part  of  the  direct  pyramidal  tract  (N.  11,  Add.). 

Antero-lateral  Ascending  Cerebellar  Tract. ^'^ — Taking  its 

(35)  Fasciculus  proprius   antero-lateralls. 

(36)  Tractus  triangrularis  (Helwlgi). 

(37)  Fasciculus  antero-lateralis  superficialis,  descendens  and  as- 
cendens. 


142  THE    BRAIN   AND    SPINAL    CORD. 

origin  from  the  base  of  the  anterior  cornu  and  center  of  the 
crescent  of  gray  matter,  chiefly  on  the  opposite  side  of  the 
spinal  cord,  and  crossing  through  the  anterior  commissure,  it 
ascends  mingled  with  the  fibers  of  the  above  descending  tract, 
along  the  lateral  surface  of  the  cord.  It  runs  along  the 
dorso-lateral  groove  and  through  the  formatio  reticularis 
of  the  medulla  and  pons;  and  then,  turning  backward,  it 
reaches  the  superior  cerebellar  worm  through  the  valve  of 
Vieussens.  A  small  bundle  of  its  fibers  winds  over  the  su- 
perior cerebellar  peduncle,  and  joins  the  lateral  fillet  in  its 
course  to  the  inferior  quadrigeminal  body;  that  bundle  ends 
in  the  optic  thalamus.  The  antero-lateral  ascending  cere- 
bellar tract  is  closely  related  to  the  direct  cerebellar  tract. 
Both  carry  sensory  impulses  to  the  vermis  cerebelli  superior, 
though  from  different  parts  of  the  cord. 

The  Crossed  Descending  Tract  of  the  Red  Nucleus,  running 
dorsal  to  the  inferior  olive,  is  mingled  with  the  fibers  of  the 
antero-lateral  ascending  cerebellar  tract,  in  the  medulla;  it 
continues  down  the  cord,  in  the  dorso-lateral  portion  of  the 
crossed  pyramidal  tract,  to  the  lateral  horn  and  center  of  the 
gray  crescent  as  far  as  the  first  lumbar  segment. 

POSTERIOR  AREA. 

The  longitudinal  fibers  of  the  posterior  area  form  many 
bundles;  and  the  bundles  are  different  in  upper  and  lower 
medulla.  The  formatio  reticularis  is  small,  but  is  present 
throughout  this  area. 

The  lower,  or  closed,  medulla  contains:  The  Fasciculus 
gracilis,^^  Fasciculus  cuneatus,^^  Fasciciilus  of  Eolando  and 
Direct  cerebellar  tract  (named  from  the  posterior  median 
fissure  outward).     In  the  upper  or  ventricular  medulla  are: 

(38)  Fasciculus  gracilis. 

(39)  Fasciculus  cuneatus. 


THE    AFTER-BKAIN.  143 

The  Restiform  body,  at  the  surface;  and  the  Inferior  (or 
spinal)  root  of  the  fifth  cranial  nerve,  the  Fasciculus  soli- 
tarius  and  Fasciculus  teres  in  the  interior. 

The  Fasciculus  Gracilis  is  the  superior  end  of  the  postero- 
median column  (GolFs  column)  of  the  spinal  cord.  Near 
its  extremity  it  expands  and  forms  the  clava,  and  then  tapers 
off  and  disappears  along  the  side  of  the  fourth  ventricle.  The 
clava  is  due  to  the  nucleus  gracilis,  in  which  the  fibers  of 
the  column  end.  A  small  number  of  fibers  continue,  without 
interruption,  into  the  fillet  and  external  arciform  fibers. 
Like  the  cuneate  column,  the  fasciculus  gracilis  is  composed 
of  ascending  branches  of  the  posterior  roots  of  the  spinal 
nerves. 

Fasciculus  Cuneatu^. — It  is  'separated  from  the  posterior 
median  fissure  by  the  gracile  bundle ;  and  is  the  continuation 
of  the  greater  portion  of  the  postero^lateral  column  (Bur- 
dach's  column)  of  the  spinal  cord.  It  ends  about  the  cells 
of  the  nucleus  cuneatus  and  accessory  nucleus  cuneatus,  which 
form  the  cuneate  tubercle  seen  on  the  surface.  A  few  fibers 
from  this  bundle  are  directly  continued  in  the  interolivary 
fillet,  and  two  small  bundles,  inclosing  the  inferior  (or 
spinal)  root  of  the  fifth  nerve,  run  as  posterior  external  ai-ei- 
form  fibers  to  the  cerebelliun.  The  fibers  of  the  fasciculus 
cuneatus*^  are  ascending  hranches  of  the  posterior  roots  of 
the  spinal  nerves. 

Fasciculus  of  Rolando. — From  the  cuneate  column,  a  small 
bundle  of  fibers,  taking  a  more  lateral  course,  runs  over  and 
ends  within  the  nucleus  of  Rolando.  It  constitutes  the  fas- 
ciculus Rolandi.  This  column  is  not  separately  represented 
in  the  spinal  cord.  The  nucleus  of  Rolando,  in  which  it 
terminates,   is  situated  beneath  the  restiform   body.      The 

(40)    Fasciculus  cuneatus. 


144  THE    BRAIN   AND   SPINAL    CORD. 

nucleus  causes  a  slight  eminence  on  the  surface  called  the 
tuberculum  Rolandi. 

The  Direct  Cerebellar  Tract^^  in  the  lower  medulla  crosses 
the  dorso-lateral  groove,  from  the  lateral  column  of  the  cord 
to  the  posterior  area  of  the  medulla;  it  then  ascends  to  form 
a  large  part  of  the  restiform  body,  the  inferior  peduncle  of 
the  cerebellum.  It  takes  its  origin  from  the  vesicular  col- 
umn of  Clark  in  the  spinal  cord.  It  ends  very  largely  on  the 
opposite  side  in  the  superior  cerebellar  worm. 

Restiform  Body.— In  the  upper  medulla,  forming  the 
lateral  part  of  each  posterior  area,  is  a  large  rounded  bundle 
of  fibers,  called  the  restiform  body.*^  n  jg  the  largest 
bundle  in  the  medulla.  Forming  the  inferior  peduncle  of  the 
cerebellum,  it  terminates  in  the  cerebellar  cortex  of  both  the 
hemisphere  and  worm.  It  is  made  up  of  the  following: 
Ascending — (1)  Direct  cerebellar  tract;  (2)  External  arci- 
form  fibers,  anterior  and  posterior;  (3)  The  acustico-cere- 
bellar  tract  from  the  nuclei  of  the  vestibular  nerve  to  the 
nucleus  fastigii  and  nucleus  globosus  of  the  opposite  side; 
and  (4)  A  tract  from  the  lateral  nucleus  to  the  same  side 
of  the  cerebellum.  Descending — (1)  Antero-lateral  descend- 
ing cerebellar  tract,  and  (2)  The  cerebello-olivary  tract, 
which  ends  in  the  inferior  olive  opposite  to  its  origin. 

The  restiform  bodv  is  inclosed  between  the  medial  and 
lateral  roots  of  the  auditory  nerve  (eighth ).*3  Yentral  to 
it  and  between  the  roots,  is  the  ventral  part  of  the  cochlear 
nucleus;  on  its  lateral  surface  and  among  the  fibers  of  the 
lateral  root,  is  the  dorsal,  or  lateral,  part  of  the  same 
nucleus.  The  vestibular  nuclei,  the  dorso-medial  (Schwalbe), 
the  dorso-lateral   (Deiter),  and  the  superior   (Flechsig  and 

(41)  Fasciculus   cerebello-spinalls. 

(42)  Corpus  restiforme. 

(43)  Nervus  acusticus. 


THE    AFTER-BRAIN.  I45 

Beehterew)  are  situated  dorsal  and  medial  to  the  restiform 
body. 

The  Inferior  Root  of  the  Fifth  Nerve^^  is  the  main  sensory 
root.  It  leaves  the  superior  sensory  root  in  the  pons;  and, 
running  down  in  the  lateral  portion  of  the  posterior  area,  it 
terminates  ventral  to  the  restiform  body  about  the  cells  of 
the  nucleus  Rolandi. 

Fasciculus  Solitarius. — The  respiratory  bundle  is  a  small, 
round  bundle  imbedded  in  the  middle  of  the  ventricular  gray 
matter  of  the  posterior  area.  It  forms  an  accessory  sensory 
root  for  the  ninth  and  tenth  cranial  nerves.  It  descends  near 
the  main  nuclei  of  those  nerves  and  along  the  medial  aspect 
of  the  posterior  horn  of  gray  matter  in  the  cord.  It  ends  on 
both  sides  of  the  median  line  in  the  gray  matter  along  its 
course.  The  solitary  bundle  may  be  traced  from  the  upper 
part  of  the  medulla  down  to  the  eighth  cervical  segment  of 
the  spinal  cord  (Cajal).  Many  of  its  fibers  cross  through 
the  raphe  and,  after  giving  off  collaterals  to  the  interolivary 
fillet,  terminate  about  cells  on  the  opposite  side.  It  is  be- 
lieved to  associate  the  nuclei  of  the  nerves  controlling  the 
muscles  of  respiration,  hence  the  synonym,  respiratory 
bundle. 

Fasciculus  Teres. — On  either  side  of  the  median  line  and 
extending  almost  the  whole  length  of  the  floor  of  the  fourth 
ventricle,  is  a  lozenge-shaped  eminence,  called  the  fasciculus 
teres.  In  the  pontine  part  of  the  ventricular  floor,  it  ends  as 
the  eminentia  teres.  It  tapers  off  to  a  point  in  the  posterior 
angle  of  the  ventricle  (hypoglossal  trigone),  and  the  two 
fasciculi  form  the  nibs  ol  a  pen,  the  calamus  scriptorium.  It 
is  composed  of  a  flat  band  of  fibers  covering  the  hypoglossal 
nucleus,  posteriorly,  and  the  terete  and  the  abducent  nucleus, 

(44)    Radix   spinalis   nervi   trigemini 


146  THE    BRAIN    AND    SPINAL    CORD. 

anteriorly.  The  ascending  portion  (genu)  of  the  root  of  the 
facial  (or  7th)  nerve  and  fibers  from  the  forma tio  reticularis 
make  up  the  fasciculus  teres. 

*-      GRAY   MATTER   OF   MEDULLA. 

The  gray  matter  of  the  medulla  is  composed,  (1)  .of  that 
continued  up  from  the  spinal  cord,  and  (2)  of  addS  nuclei 
not  represented  in  the  cord. 

(1)  By  the  dilation  of  the  central  canal  of  the  spinal 
cord  forming  the  fourth  ventricle,  the  posterior  comua  of 
the  H-shaped  column  of  gray  matter  are  pushed  outward  to 
a  transverse  direction;  and  the  bases  of  the  anterior  cornua 
are  brought  into  the  floor  of  the  ventricle.  The  expansion 
of  the  canal,  together  with  the  decussation  of  the  crossed 
pyramidal  tracts  through  the  anterior  cornua  and  of  the  in- 
terolivary  fillets  through  the  posterior  and  anterior  cornua, 
disposes  the  H-shaped  Column  as  follows: 

Anterior  Horn. — From  the  base  of  the  anterior  cornu*^  is 
derived  a  column  of  cells,  the  hypoglossal  nucleus,  which 
lies  along  the  median  raphe  beneath  the  fasciculus  teres. 
The  head  of  the  anterior  cornu  is  broken  up  by  the  crossed 
pyramidal  tract  into  the  nucleus  later-alis,  in  the  lateral  area, 
near  the  dorso-lateral  groove;  and  the  nucleus  amhiguus,  a 
large  column  of  cells,  coinciding  in  extent  with  the  inferior 
olive,  and  seen  as  a  pear-shaped  mass  in  the  lateral  area, 
which  is  the  motor  nucleus  for  the  ninth,  tenth  and  access- 
ory part  of  the  eleventh  cranial  nerves.  The  lateral  nucleus 
is  probably  terminal  to  certain  fibers  in  the  antero-lateral 
ascending  cerebellar  tract,  and  it  gives  rise  to  a  tract  of  fibers 
which  runs  through  the  restiform  body  to  the  cortex  in  the 
same  side  of  the  cerebellum.  The  gray  matter  of  the  formatio 
reticularis  alba  et  grisea  belongs  to  the  anterior  cornu.  It  is 
(45)    Columna  anterior. 


THE   AFTER-BRAIN.  147 

of  a  light  color  (alba)  in  the  anterior  area,  where  there  are 
the  bodies  of  but  few  cells.  In  the  lateral  area  the  cell- 
bodies  are  numerous  and  the  color  is  gray  (grisea). 

The  Posterior  Horn^^  is  decapitated  by  the  fillet.  Its 
base  forms  a  column  of  cells,  external  to  the  nucleus  am- 
biguus  and  hypoglossal  nucleus,  which  contains  the  chief 
sensory  nucleus  of  the  pneumo gastric  (lOth),  of  the  glosso- 
pharyngeal (9th),  and  of  a  part  of  the  auditory  (8th)  nerves. 
It  forms  likewise  the  accessory  cuneate  nucleus.  The  head 
of  the  posterior  horn  forms  the  nucleus  of  Rolando.  That 
nucleus  is  the  inferior  sensory  nucleus  of  the  trifacial  (5th) 
nerve.  In  it  the  so-called  ascending  root  of  the  fifth 
terminates.  The  posterior  horn  furnishes  the  gray  matter 
for  the  reticular  formation  of  the  posterior  area. 

It  should  be  noted  that  the  chief  nuclei  derived  from  the 
H-shaped  column  lie  in  the  floor  of  the  fourth  ventricle. 

(2)  Added  Nuclei. — The  medullary  gray  matter  not  rep- 
resented in  the  spinal  cord  makes  up  the  following  nuclei: 
Nucleus  gracilis,  nucleus  cuneatus,  olivary  nuclei,  and  nu- 
cleus of  external  arciform  fibers. 

Nucleus  Gracilis  and  Nucleus  Cuneatus. — They  are  situ- 
ated near  the  dorsal  surface  of  the  medulla,  beneath  the  gra- 
cile  and  cuneate  bundles,  whose  fibers  terminate  in  them : 
they  give  origin  to  the  interolivary  fillet  and  the  anterior 
and  posterior  external  arciform  fibers,  the  two  former  con- 
stituting the  sensory  decussation;  and  they  produce,  re- 
spectively, the  clava  and  cuneate  tuhercle.'^'^  The  accessory 
cuneate  nucleus  is  a  continuation  of  the  vesicular  column  of 
Clark  at  the  base  of  the  posterior  gray  horn  in  the  spinal 
cord.     From  it  a  small  fasciculus  rises  which,  as  posterior 

(46)  Columna  posterioF. 

(47)  Tuberculum  cuneatum.  . 


148  THE    BRAIN    AND    SPINAL    CORD, 

external  arciform  fibers,  runs  within  the  restiform  body 
to  the  eerebellnm.  The  nucleus  gracilis  and  cuneatus  are 
connected  with  the  posterior  cornu,  but  have  no  representa- 
tive in  the  cord. 

The  Olivary  Nucleus^^  of  the  medulla  (inferior  olivary 
nucleus)  is  a  sinuous,  pouch-like  collection  of  gray  matter 
resembling  the  corpus  dentatum  of  the  cerebellum.  It  is 
situated  near  the  lateral  surface  of  the  medulla  and  is  in- 
vested superficially  and  deeply  by  fibers  from  the  antero- 
lateral ground  bundle.  Its  open  hilum  looks  medially  and 
is  filled  with  fibers,  the  cerebello-olivary  tract/^  which  join 
it  to  the  opposite  hemisphere  of  the  cerebellum.  On  either 
side  of  the  olivary  nucleus  is  an  accessory  nucleus — the  in- 
ternal accessory,^^  in  the  anterior  area  among  the  fibers  of 
the  inter-olivary  fillet,  and  the  external  accessory,^^  in  the 
lateral  area.  The  olivary  nucleus,  covered  by  fibers  of  the 
antero-lateral  ground  bundle,  forms  the  olivary  body  (oliva). 
The  triangular  tract  of  Helwig,  or  the  olivary  bundle  of  the 
spinal  cord,  enters  the  ventral  surface  of  the  olivary  body 
and  is  believed  to  terminate  in  it.  The  olivary  bundle  of  the 
brain,  the  central  tegmental  tract,  appears  to  rise  from  the 
olive  in  the  medulla  and  to  continue  the  ascending  conduction 
tract  to  the  globus  pallidus  of  the  lenticular  nucleus 
(Flechsig).  The  latter  tract  is  situated  just  dorsal  to  the 
olive.  The  inferior  olive  receives  two  tracts  of  descending 
fibers,  namely,  the  vestibulo-olivary  and  the  cerebello-olivary. 
And  according  to  Koelliker,  it  gives  origin  to  axones  which 
descend  through  the  lateral  column  of  the  spinal  cord  to  the 
anterior  gray  cornu. 

(48)  Nucleus  olivaris  inferior. 

(49)  Pibrse   cerebello-olivares. 

(50)  Nucleus  olivaris  accessorius  medialis. 

(51)  Nucleus  olivaris  accessorius  dorsalis. 


THE    AFTER-BRAIN.  149 

Nucleus  of  the  External  Arciform  Fibers. — There  are  sev- 
eral masses  of  gray  matter,  containing  the  bodies  of  nerve 
cells,  scattered  among  the  anterior  external  arciform  fibers. 
These  form  a  large  sheet-like  mass  on  the  ventral  and  medial 
surface  of  the  pyramid.  It  is  called  the  arciform  nucleus,^^ 
and  probably  constitutes  a  relay  for  certain  of  the  anterior 
external  arciform  fibers.  The  arciform  nucleus  is  continuous 
above  with  the  nucleus  pontis. 

Lesions  in  the  medulla  are  very  fatal  and  death  usually 
occurs  before  any  sensory  or  motor  phenomena  can  be  ob- 
served; but  rarely  the  pyramidal  tracts  alone  have  been  in- 
volved or  the  pyramidal  tracts  together  with  one  or  more  of 
the  roots  of  the  ninth  to  the  twelfth  cranial  nerves.  In  the 
last  case,  crossed  paralysis  is  produced,  affecting  the  cranial 
nerves  on  the  same  side  and  the  opposite  spinal  nerves.  In 
progressive  bulbar  paralysis  the  motor  nuclei  of  the  medulla 
are  involved  as  "a  preliminary  to  the  degeneration  of  the  an- 
terior gray  cornu  in  the  spinal  cord  ( Grlossolabio-laryngeal 
paralysis). 

(52)    Nucleus  arcuatus. 


CHAPTER    VII. 


FOURTH   VENTRICLE. 

The  common  cavity  of  the  hind-brain  and  after-brain  is 
the  fourth  ventricle.^  The  fourth  ventricle  is  contained  in 
the  pons  and  medulla,  and  is  ventral  to  the  cerebellum.  It 
is  broadest  at  the  junction  of  the  pons  and  medulla.  Above 
and  below  that  junction,  it  contracts  to  the  size  of  the  aque- 
duct of  Sylvius  and  central  canal  of  the  spinal  cord,  with 
which  it  is  continuous.  Dorsally,  it  communicates  with  the 
subarachnoid  space  through  three  foramina  (Magendie,  and 
Key  and  Retzius).  It  is  a  gable-roofed  chamber  with  a  dia- 
mond-shaped floor.  The  long  axis  of  the  floor  is  parallel 
with  the  spinal  cord,  and  extends  from  the  superior  extrem- 
ity of  the  pons  to  the  middle  of  the  medulla.  The  trans- 
verse axis  coincides  with  the  junction  of  the  pons  and 
medulla.  Thus  the  superior  triangle  of  the  floor  is  formed 
by  the  pons;  the  inferior,  by  the  medulla  oblongata.  The 
fourth  ventricle  is  lined  with  ependyma,  which  is  complete 
throughout,  except  in  the  roof  of  the  inferior  part,  where 
only  the  epithelial  layer  is  present. 

Boundaries. — The  floor  is  formed  by  the  pons  and  me- 
dulla. The  lateral  walls  (superior  triangle)  are  formed  by 
the  superior  peduncles^  of  the  cerebellum;  and  (inferior  tri- 
angle) by  the  inferior  cerebellar  peduncles,^  fasciculus 
cuneatus  and  fasciculus  gracilis.  The  roof  is  formed  by  the 
valve  of  Vieussens,*  superiorly;  and  the  inferior  medullary 

(1)  Ventriculus  quartus.  (3)    Corpora  restiformia. 

(2)  Brachia  conjunctiva.  (4)    Velum  medullare  anterius. 


FOURTH    VENTRICLE.  I5I 

velum  and  roof  epithelium,  inferiorly.  The  superior  and 
inferior  halves  of  the  roof  meet  at  an  acute  angle  and  form 
the  tent^  of  the  fourth  ventricle.  On  either  side,  the  tent 
extends  over  the  restiform  body  into  the  lateral  recess.  The 
lateral  recess  is  a  tunnel-like  extension  of  the  ventricular 
cavity.  It  is  bounded,  superiorly  and  ventrally,  by  the  in- 
ferior cerebellar  peduncle;  dorsally,  by  the  inferior  medul- 
lary velum;  and  inferiorly,  by  the  roof  epithelium.  The 
choroid  plexuses^  of  the  fourth  ventricle  invaginate  the  roof 
epithelium  and  hang  from  the  roof  in  the  posterior  part  of 
the  cavity. 

Floor  of  the  Fourth  Ventricle. — Because  of  the  origin  of 
one  or  more  roots  of  the  posterior  eight  (fifth  to  twelfth) 
cranial  nerves  from  the  floor  of  the  fourth  ventricle,  it  is 
a  very  important  area.  A  median  groove'''  forming  the  long 
axis  of  the  diamond-shaped  floor,  divides  it  in  two  lateral 
halves,  which  are  bisected  transversely  by  a  number  of  lines, 
the  acustic  striae.^  The  acustic  striae  are  produced  by  bundles 
of  fibers  which  rise  from  the  cochlear  root  in  part,  but  chiefly 
from  the  cochlear  nucleus  of  the  auditory  nerve.  Plunging 
into  the  median  groove,  the  greater  number  enter  the  oppo- 
site trapezium  and  lateral  fillet;  the  remainder,  according  to 
Koelliker,  become  anterior  external  arciform  fibers.  The 
acustic  strias  divide  each  lateral  half  of  the  floor  into  a  su- 
perior and  an  inferior  triangle. 

The  Superior  Triangle  of  the  floor  presents  the  eminentia 
teres,  superior  fovea,  locus  coeruleus  and  a  part  of  the  acustic 
trigone. 


(5)  Fastigium. 

(6)  Plexus  choroideus  ventriculi  quartl. 

(7)  Sulcus  longitudinalis  fossse  rhomboidese. 

(8)  Striae  medullares. 


152  THE    BRAIN    AND    SPINAL    CORD. 

The  Emi/nentia  Teres,^  the  anterior  extremity  of  the  fascic- 
Tilus  teres/ ^  is  located  next  the  median  groove.  Beneath 
it  are  the  nucleus  teres  (accessory  to  ninth  and  tenth  cranial 
nerves),  and  nucleus  of  the  abducent  (sixth)  nerve.  Ex- 
ternal to  it  and  in  front  of  the  striae  acusticae  is  a  small  fossa, 
the  fovea  superior.    , 

The  Fovea  Superior. — The  fovea  superior  is  near  the  lat- 
eral wall  of  the  ventricle  and  marks  the  location  of  the  facial 
(seventh)  nucleus,  which  is  deeply  seated  in  the  pons.  Run- 
ning forward  and  medially  along  the  wall  of  the  ventricle 
from  the  superior  fovea,  is  a  blue-floored  groove,  called  locus 
coeruleus. 

The  Locus  Coeruleus  continues  to  the  anterior  angle  of 
the  ventricle.  The  color  of  the  locus  coeruleus  is  due  to  the 
substantia  ferruginea,  a,  pigmented  layer  of  cell-bodies  un- 
derlying it.  The  principal  motor  nucleus  of  the  trifacial, 
or  fifth,  nerve  lies  beneath  the  anterior  part  of  the  locus 
coeruleus. 

Inferior  Trianglei  of  the  Ventricular  Floor. — It  presents: 
The  hypoglossal  trigone,  trigonum  vagi  (fovea  inferior,  ala 
cinerea  and  eminentia  einerea)  and  most  of  the  trigonum 
acustici. 

The  Hypoglossal  Trigone^'^  is  the  inferior  half  of  the  fas- 
ciculus teres.  Its  apex  is  in  the  inferior  angle  of  the  ven- 
tricle, and  forms  a  nib  of  the  calamus  scriptorius;  its  base 
looks  upward  and  is  situated  under  the  acustic  striae.  The 
twelfth  nerve  rises  from  the  column  of  cells  covered  by  it. 
External  to  the  trigonum  hypoglossi  and  inferior  to  the 
acustic  striae  is  the  inferior  fovea,  which  forms  the  apex  of 
the  trigonum  vagi. 

(9)  Colliculus  facialis. 

(10)  Eminentia  medlalis. 

(U)    Trlgronmn  nervl  hyposlosst 


FOURTH   VENTRICLE.  I  53 

Trigonum  Vagi. — The  pneumogastric  trigone  is  of  a 
darker  color  than  the  ventricular  floor  around  it,  and  is  often 
called  the  ala  cinerea.  The  inferior  fovea  forms  the  de- 
pressed and  superiorly  directed  apex  of  the  triangle ;  its  floor 
rises  inferiorly  to  the  base,  eminentia  cinerea,  which  abuts 
against  the  lateral  wall  of  the  ventricle.  The  principal 
nuclei  of  the  glosso-pharyngeal  (or  ninth)  and  the  pneumo- 
gastric (or  tenth)  nerves  are  situated,  respectively,  beneath 
the  fovea  inferior  and  trigonum  vagi. 

The  Trigonum  Acustici^^  occupies  the  lateral  angle  of  the 
ventricular  floor.  It  is  partly  in  the  superior  triangle,  but 
chiefly  in  the  inferior.  Inclosed  between  the  trigonum  vagi 
and  the  ligula,  its  apex  points  downward,  and  its  base  looks 
upward  and  is  crossed  by  the  acustic  striae.  A  slight  tuber- 
cle, eminentia  acusticce,  makes  the  base  of  the  trigone,  in 
the  lateral  angle  most  prominent.  Beneath  the  acustic  tri- 
gone is  the  dorsal,  or  vestibular,  nucleus  of  the  auditory 
nerve;  also  the  dorsal  part  of  the  cochlear  nucleus,  which  is 
found  in  the  acustic  tubercle. 

ORIGIN  OF  CRANIAL  NERVES. 

According  to  Soemmering,  there  are  twelve  pairs  of  cranial 
nerves.  Their  origins  (or  terminations)  are  superficial  and 
deep.  The  meaning  of  Superficial  (apparent)  origin,  as 
commonly  used,  is  the  point  of  attachment  of  a  nerve  to  the 
brain  or  cord  surface;  Deep  (real)  origin  signifies  the  deep- 
est point  to  which  the  fibers  of  a  nerve  can  be  traced.  For 
Motor  Nerves  this  nomenclature  is  correct,  the  deep  origin 
being  the  nucleus  in  which  the  fibers  rise  that  form  the 
nerve;  but  it  is  exactly  opposite  to  the  truth  for  Sensory 
Nerves.  The  so-called  deep  origin  of  a  sensory  nerve  is 
actually  the  terminal  nucleus  in  which  the  fibers  of  the  nerve 

(12)    Area  acustica. 


154 


THE    BRAIN    AND   SPINAL    CORD. 


arborize  and  end.     With  these  facts  in  mind  examine  the 
following  table   (N.   12,  Add.). 


Name. 


1.  Olfactory". 
(Smell) 


TABLE  II. 

Superficial  origin, 
or  termination. 


Deep  origin,  or 
termination. 


Nerves  .  Olfactory  f  Stratum  glomeru- 
bulb,  surface  •  •  •  "S       losum  of  olf ac- 
.    L      tory  bulb. 

Gyrus   fornicatus. 

Trigonum  olfac- 
torii. 

Uncus  hippocam- 
pi. 


Tract. Three  roots 


2.  Optic".... 
(Sight) 


Nerve.  Optic 
commissure . . . 


Optic  tha- 
lamus, ex- 
ternal and 
internal 
geniculate 
bodies,  an- 
t  e  r  i  o  r 
q  uad  r  i- 
geminal 
body 


Tract 


3.  Oculomotor". 
(Motor) 


4.  Trochlear". 
(M.) 


Interpeduncular 
fossa 


Outer  root — Ex- 
ternal geniculate 
body,  optic  tha- 
lamus, Anterior 
quadrigeminal 
body. 

Inner  root — Optic 
thalamus,  Inter- 
nal geniculate 
body. 

Floor  of  Sylvian 
aqueduct. 


Valve    o  f 
sens  . . . 


Vieus 


{ 


Floor  of   Sylvian 
aqueduct. 


(13)  Nervus  olfactorius. 

(14)  Nervus  opticus. 


(15)  Nervus  oculomotorius. 

(16)  Nervus  trochlearis. 


FOURTH    VENTRICLE, 


155 


5.  Trifacial".... 
(M.  Sensory) 


6.  Abducent". 
(M.) 


7.  Facial" 
(M.) 


Pars  intermedia-". 
(Taste) 


Pons,  ventral  sur- 
face   


Groove  between 
pons    and    me- 
dulla   


Groove  between 
pons    and    me- 
dulla   


Between  facial 
and  auditory. 


8.  Auditory^^ 

(Hearing  and 
space-sense) 


{ 


Groove  between 
pons    and    me- 
dulla  , 


Motor  root — Floor 
of  fourth  ventri- 
cle, and  Sylvi- 
an aqueduct. 

Sensory  root — 
Under  superior 
cerebellar  pe- 
duncle in  pons, 
and  Nucleus  of 
Rolando  in  me- 
dulla. 

Floor  of  fourth 
ventricle  be- 
neath eminentia 
teres. 

Floor  o  f  fourth 
ventricle  be- 
neath superior 
fovea. 

Beneath  inferior 
fovea. 
r  Vestibular  root — 
Vestibular  (or 
Dorsal)  nucleus 
in  ventricular 
floor,  Spinal  nu- 
cleus in  cord. 
Nucleus  fastigii 
and  nucleus  glo- 
bosus  in  cerebel- 
lum. 

Cochlear  root — 
Cochlear  (or 
ventral)  nucle- 
us (ventral  and 
dorsal  parts)  in 
dorso -  lateral 
groove  and  on 
lateral  surface  of 
restiform  body, 
and  various  nu- 
clei up  to  pos- 
terior quadri- 
geminal  body. 


(17)  Nervus   trigeminus. 

(18)  Nervus  abducens. 

(19)  Nervus  facialis. 


(20)  Nervus  intermedius, 

(21)  Nervus  acustious. 


156  THE    BRAIN    AND    SPINAL    CORD. 


9.  Glossopharyngeal^^  <^       groove    of   me-      Ventricular   floor, 
(M.  S.  and  I       dulla J      posterior    trian- 


{Dorso-lateral  .  ^ 
groove    of   me- 
dulla   <j 

{Dorso-lateral 
groove    of  me-  ( 
dulla <^ 

{Dorso-lateral 
groove    of   me-  ( 
dulla <^ 

J   Lateral  column  of  r 
*j       spinal  cord J 

{Ventro-lateral 
groove    of   me-  r 
dulla J 


taste)  gle   beneath    fo- 

.   Dorso-lateral  '^     ^^^  i^^^^^^^' 

10.  Pneumogastric^ 
(M.S.)  [      dulla <^  Ventricular    floor, 

trigonum  vagi. 

11.  Spinal  acces^ory^ 
(M.)  f  Dorso-lateral 

Accessory  root-  _____ 

dulla  .... . .  i  Closed  medulla. 

a^.   „,  ^«^4.28             I   --"-i.v.xc^x  v.«x^*xx.x  v,^  I   Intermedio  -  later- 
Spinal  root- ^       gp.^^i  ^^^^ J      ^1    column    of 

cells  in  cord. 


Ventro-lateral 

12.  Hypoglossal" <]       groove    of   me-  r  ventricular    floor 

(M.)  i      dulla <|      beneath  trigo- 

num hypoglossi. 


The  posterior  ten  cranial  nerves  rise  from  two  series  of 
nuclei — (1)  a  ventral  or  anterior  and  (2)  a  dorsal  or  poste- 
rior series.  The  ventral  series  corresponds  to  the  anterior 
cornn  of  gray  matter  in  the  spinal  cord.  It  is  entirely  motor 
and  genetic.  The  dorsal  is  regarded  as  a  continuation  of  the 
posterior  cornu  and  is  sensory  in  function  and  terminal. 
Each  series  is  composed  of  a  double  chain  of  nuclei :  (a)  A 
medial  chain^  derived  from  the  base  of  the  cornu  and  (b)  a 
lateral  chain,  from  the  caput  cornu. 

(1;)     Ventral  Series,  Motor 
(a)     The  Medial  Chain  is  close  to  the  median  line,  be- 
neath the  fasciculus  teres  and  aqueduct  of  Sylvius.    It  gives 
origin  to  the  Hypoglossal   (12th),  Abducent  (6th),  Troch- 
lear (4th),  and  Oculomotor  (3rd)  nerves;  also  to  accessory 

(22)  Nervus  glossopharyngeus.  (25)    Radix  cerebralis. 

(23)  Nervus  vagus.  (26)    Radix  spinalis. 

(24)  Nervus  accessorius.  (27)    N.  hypoglossus. 


FOURTH    VENTRICLE.  157 

motor  roots  of  the  lOtli  and  9tli  nerves  in  the  nucleus  teres; 
and  to  the  5th  in  the  floor  of  the  Sylvian  aqueduct.  All  are 
efferent  or  motor. 

(b)  Lateral  Chain. — This  also  is  motor.  It  lies  external 
to  the  medial  chain,  beneath  the  internal  parts  of  the  locus 
eoeruleus  and  trigonum  vagi.  Converging  slightly  toward 
its  fellow  of  the  opposite  side  it  extends  downward  into  the 
closed  medulla.  It  is  regarded  as  the  head  of  the  anterior 
cornu.  From  the  lateral  chain  of  the  ventral  series  rise: 
The  accessory  root  of  the  spinal  accessory  (11th),  posterior 
to  the  fourth  ventricle ;  the  chief  motor  roots  of  the  Pneumo- 
gastric  (10th)  and  Glosso-pharyngeal  (9th) ;  the  root  of  the 
Facial  (7th) ;  and  the  principal  motor  root  of  the  Trifacial 
(oth).  The  motor  roots  of  the  11th,  10th  and  9th  nerves 
rise  from  the  nucleus  ambiguus. 

(2)     Dorsal  Series,  Sensory. 

(a)  Medial  Chain  of  Nuclei. — It  corresponds  to  the  base 
of  the  posterior  gray  cornu.  Placed  external  to  the  ventral 
series,  it  is  covered  by  the  lateral  part  of  the  trigonum  vagi, 
the  acustic  trigone  and  superior  peduncle  of  the  cerebellum. 
It  is  entirely  sensory  and  terminal,  and  it  contains  the  princi- 
pal sensory  nuclei  of  the  Pneumogastric  (10th),  and  Glosso- 
pharyngeal (9th) ;  the  dorsal  (vestibular)  nucleus  of  the 
Auditory  (8th)  ;  and  the  superior  sensory  nucleus  of  the 
Trifacial  (5th). 

(b)  The  Lateral  Chain  of  the  dorsal  series  is  most  ex- 
ternal in  position.  It  is  located  beneath  the  tubercle  of 
Rolando  and  the  restiform  body.  In  it  are  contained  the 
inferior  sensory  nucleus  of  the  trifacial  (5th),  called  the 
nucleus  of  Rolando;  and  the  ventral  (accessory)  and  lateral 
nuclei  (the  cochlear  nuclei)  of  the  eighth,  or  auditory,  nerve. 
These  nuclei  are  sensory,  or  afferent,  and  terminal. 


158  THE    BRAIN   AND    SPINAL    CORD. 

The  Olfactory  (1st)  and  the  Optic  (2iid)  are  sensory,  or 
afferent^  and  probably  belong  to  the  dorsal  nerves,  but  this 
is  difficult  of  demonstration. 

BLOOD   SUPPLY   OF   THE   MEDULLA   OBLONGATA. 

Branches  of  the  posterior  inferior  cerebellar  artery,  the 
vertebral  and  the  anterior  spinal  supply  the  medulla.  The 
first  supplies  the  choroid  tela.  The  branches  to  the  nerve 
substance  enter  the  median  raphe  or  follow  the  roots  of  the 
bulbar  nerves,  suggesting  the  centrifugal  and  centripetal 
arteries  of  the  spinal  cord.  The  veins  pursue  the  same  course 
as  the  arteries.  Both  arteries  and  veins  possess  the  perivascu- 
lar lymph  spaces.    There  are  no  lymphatic  vessels. 


CHAPTER   VIII. 


MEMBRANES    OF   THE    SPINAL   CORD. 

Dura  Mater. — Through  the  foramen  magnum  the  mem- 
branes of  the  cord  are  continuous  with  those  of  the  brain, 
with  which  they  are  very  similar  in  structure.  The  dura 
mater^  is  attached  to  the  margin  of  the  great  foramen  and 
to  the  bodies  of  the  first  two  or  three  cervical  vertebrae;  else- 
where its  surface  is  free  from  bony  attachment  and  does  not 
possess  the  periosteal  layer.  Thus  suspended,  it  hangs  as  an 
open  sack,  or  sheath,  and  reaches  down  to  the  third  sacral 
vertebra,  where  it  is  contracted  to  a  fibrous  cord  which  blends 
with  the  periosteum  on  the  posterior  surface  of  the  coccyx. 

The  spinal  cord  and  the  cauda  equina  are  contained  in  the 
dural  sack.  Externally,  the  surface  of  the  dura  is  separated 
from  the  wall  of  the  spinal  canal  by  the  meningonrachidian 
veins,2  areolar  tissue  and  fat.  It  is  composed  of  flat  polyg- 
onal cells,  like  the  inner  surface.  Its  internal,  serous  sur- 
face is  bathed  with  a  small  amount  of  eerebro-spinal  fluid 
which  separates  it  from  the  Arachnoid.  For  every  segment 
of  the  spinal  cord,  it  presents,  on  either  side,  a  pair  of  foram- 
ina, through  which  run  the  anterior  and  posterior  roots, 
of  the  spinal  nerves.  Those  nerve  roots  are  invested  by  a 
sheath  of  dura  prolonged  from  the  margins  of  the  foramina. 
The  dura  mater  of  the  cord  does  -not  separate  into  two  layers 
and  forms  neither  sinuses  nor  processes.     It  performs  no 

(1)  Dura  mater  spinalis. 

(2)  Plexus  venosi  vertebrales  internl. 


l60  THE    BRAIN   AND    SPINAL    CORD. 

periosteal  function  and  possesses  no  Pachionian  bodies.  Its 
two  surfaces  ar^  formed  by  endothelium. 

Arachnoid. — The  arachnoid^  of  the  spinal  cord  forms  a 
sack  of  the  same  length  as  the  dural  sheath,  with  which  it  is 
externally  in  contact.  It  presents  two  serous  surfaces.  In- 
ternally, bands  of  fibro-elastic  tissue  attach  it  to  the  pia 
mater,  and  form  the  posterior  fenestrated  septum.^  The 
meduUi-spinal  veins^  and  a  considerable  space  separate  the 
arachnoid  from  the  pia  mater.  That  subarachnoid  space  is 
filled  with  fluid.  By  the  ligamenta  denticulata  it  is  divided 
into  the  anterior  and  posterior  svbaraclinoid  spaces,^  which, 
through  the  foramen  magnum,  are  continuous  with  the  same 
spaces  in  the  cranial  cavity. 

Pia  Mater.— -The  pia'^  of  the  cord  is  much  stronger  than 
that  of  the  brain.  It  has  two  distinct  layers,  the  inner  of 
which  is  continuous  with  the  brain  pia  and  forms  an  epineu- 
rium  for  the  cord  and  roots  of  the  spinal  nerves.  The  outer 
is  the  more  vascular  layer.  Both  layers  dip  into  the  anterior 
median  fissure;  they  form  the  anterior  septum  which  con- 
tains the  anterior  spinal  artery.  Only  the  inner  layer  is 
attached  to  the  septum  in  the  posterior  median  fissure.  The 
outer  layer  forms  the  linea  splendens  along  the  front  of  the 
cord,  and  the  lig amentum  denticulatum  on  either  side.  The 
denticulate  ligament  is  a  longitudinal  band  whose  smooth 
medial  border  is  continuous  with  the  pia  along  the  middle  of 
the  lateral  surface  of  the  cord;  its  lateral  border  is  notched 
and  its  twenty  teeth,  invested  with  arachnoid,  are  attached 
to  the  dura  opposite  the  first  twenty  vertebrae.  The  two  liga- 
ments subdivide  the  space  between  the  pia  and  arachnoid 

(3)  Arachnoidea  s?pinalls. 

(4)  Septum  subarachnoideale.  j       ,, 

(5)  Venae  spinales  externse. 

(6)  Cavum  subarachnoideale  arterius  and  posterhls. 

(7)  Pia  mater  spinalis. 


MEMBRANES   OF   THE    SPINAL    CORD.  l6l 

into  anterior  and  posterior  subarachnoid  spaces.  A  filament- 
ous extension  of  the  pia  below  the  cord  proper  forms  the 
filum  terminale.  It  descends  in  the  arachno-dural  sheath 
with  the  roots  of  the  lumbar  and  sacral  nerves,  and  all  to- 
gether constitute  the  cauda  equina.  For  some  distance  the 
filum  terminale  contains  gray  matter  and  rudimentary  fibers 
continuous  with  the  spinal  cord.  The  filum  unites  with  the 
arachnoid  and  dura:  at  the  third  sacral  vertebra  in  forming 
the  central  ligament  of  the  spinal  cord.  That  ligament  is 
inserted  into  the  coccyx.  The  pia  mater  of  the  cord  contains 
the  trunks  and  large  branches  ol  the  anterior^  and  tbe  two 
posterior  spinal  arteries,^  and  the  tributaries  of  the  medulH- 
s|>inal  veins.^°  The  membranes  of  the  spinal  cord  are  sup- 
pilied  by  recurrent  branches  of  the  spinial  nerves  and  by  ibe 
sympathetic. 

(8)  Arteria  spinalis  anteFior. 
(9),  Aa.  spinales  posteriores. 
(10)    Venae  spinales  externse. 


CHAPTER  IX. 


THE   SPINAL   CORD. 

The  spinal  cord^  is  developed  from  the  posterior  part  of 
the  neural  tube,  and  forms  the  corresponding  portion  of  the 
central  axis  of  the  nervous  system. 

Extent. — It  is  continuous  with  the  medulla  oblongata, 
above;  and,  in  the  adult,  reaches  to  the  lower  border  of  the 
first  lumbar  verticbra.  Its  length  is  seventeen  to  eighteen 
inches.  In  a  very  slender  process,  the  filum  terminale,  the 
cord  is  continued  beyond  the  first  lumbar  vertebra.  That 
process  and  the  lower  spinal  nerves  form  the  cauda  equina, 
which  is  inclosed  in  a  sheath  composed  of  the  arachnoid  and 
dura  mater.  The  filum  terminale,  for  some  distance,  con- 
tains a  prolongation  of  the  central  gray  matter  and  ventricle 
of  the  cord;  and,  also,  a  few  fibers,  which  suggest  the  coccy- 
geal nerves  of  lower  animals. 

In  the  foetus  before  the  third  month,  the  cord  and  spinal 
canal  are  of  equal  length.  At  birth  the  cord  reaches  the 
third  lumbar  vertebra,  and  it  continues  to  recede  with  the 
rapid  growth  of  the  vertebra  to  adult  life. 

Size. — ^The  spinal  cord  is  shaped  like  a  cylinder,  slightly 
flattened  from  before  backward  (dorso-ventrally).  Its  long- 
est diameter  is  transverse  and  measures  less  than  half  an 
in;ch,  except  in  the  cervical  and  lumbar  enlargements  of  the 
cord.  In  the  latter,  it  equals  a  half -inch ;  and,  in  the  former, 
it  slightly  exceeds  it.     The  thoracic  portion  of  the  cord  is 

(1)    Medulla  spinalis. 


THE    SPINAL    CORD.  E63 

small  and  nearly  cylindrical  in  shape.  Divested  of  its 
meninges  and  nerves  the  spinal  cord  weighs  about  one  ounce 
and  a  half  avoirdupois. 

The  cervical  enlargement^  extends  from  the  medulla  ob- 
longata to  the  second  thoracic  vertebra.  Its  greatest  diana- 
eter  is  on  a  level  with  the  fifth  intervertebral  disk.  It  gives 
origin  to  the  nerves  which  form  the  cervical  and  brachial 
plexuses. 

The  lumbar  enlargement^  begins  at  the  tenth  thoracic 
vertebra  and  increases  to  the  twelfth.  Opposite  the  first 
lumbar  vertebra,  it  tapers  off  almost  to  a  point,  the  conus 
iepniinalis,^  but  a  very  smadl  process  continues  in  the  filum 
terminale.  From  the  lumbar  enlargement  rise  the  nerves 
forming  the  lumbar  and  sacral  plexuses. 

Sixth  Ventricle. — ^The  central  canaP  of  the  spinal  cord  is 
the  representative  of  the  cavity  of  the  neural  tube.  It  is 
just  visible  to  the  naked  eye;  but  it  extends  throughout  the 
cord  and  expands  above  into  the  fourth  ventricle.  In  the 
filum  terminale,  it  is  also  dilated,  forming  the  inferior 
rhomhoid  fossa.^  It  is  lined  with  columnar  ciliated  cells 
which  stand  on  a  thick  lamina  of  substantia  gelatinosa 
Rolandi. 

SURFACE. 

Fissures  of  the  Spinal  Cord. — The  spinal  cord  is  incom- 
pletely divided  into  symmetrical  lateral  halves  by  the  an- 
terior and  the  posterior  median  fissure. 

The  Anterior  Median  Fissure'^  is  the  broader  and  shallower 
of  the  two.  It  extends  in  length  from  the  posterior  end  of 
the  ventral  surface  of  the  pons  (foramen  caecum  of  Yicq 
d^Azyr)   down  the  anterior  median  line  of  the  medulla  and 

(2)  Intumescentia   cervicalis.  (5)    Canalis  centralis  spinalis. 

(3)  Intumescentia  lumbalis.  (6)    Fossa  rhomboidea  inferior. 

(4)  Conus  medullarls.  (7)    Flssura  mediana  anterior. 


r64  THE    BRAIN   AND    SPINAL    CORD. 

cord,  x'^s  to  depth,  it  equals  one-third  of  the  cord's  axis.  Its 
floor  is  formed  by  the  anterior,  or  white,  commissure.  Both 
layers  of  pia  mater  dip  down  into  it  and  inclose  the  anterior 
spinal  artery  and  its  branches.  The  anterior  median  fissure 
is  interrupted  at  the  junction  of  the  cord  and  medulla  by 
the  decussation  of  the  pyramids.  In  the  lumbar  enlargement 
it  gradually  disappears. 

The  Posterior  Median  Fissure^  is  narrow  and  deep.  It 
extends,  longitudinally,  down  the  posterior  median  line  of  the 
cord  from  the  middle  of  the  dorsal  surface  of  the  medulla. 
It  divides  the  cord,  dorso-ventrally,  beyond  its  middle.  The 
floor  of  the  fissure  is  formed  by  the  posterior,  or  gray,  com- 
missure, which,  with  the  white  commissure,  separates  the 
posterior  from  the  anterior  median  fissure.  The  posterior 
median  fissure  is  occupied  by  a  lamina  of  connective  tis- 
sue, the  posterior  septum,  which  is  attached  to  the  deep 
layer  of  the  pia  mater.  In  the  posterior  septum  ramify 
branches  of  the  two  posterior  spinal  arteries  and  tributaries 
of  the  meduUi-spinal  veins. 

Postero-lateral  Fissure. — Each  lateral  half  of  the  spinal 
cord  is  partially  divided,  near  the  junction  of  the  posterior 
fourth  with  the  anterior  three-fourths  of  its  semicircumfer- 
ence,  by  the  postero-lateral  fissure.^  The  fissure  is  situated 
opposite  the  posterior  cornu  of  gray  matter,  to  which  it  trans- 
mits the  posterior  roots  of  the  spinal  nerves.  It  is  continu- 
ous above  with  the  dorso-lateral  groove  of  the  medulla.  It 
separates  the  posterior  surface  and  the  antero-lateral  sur- 
face from  each  other. 

Antero-lateral  Fissure. — It  is  convenient  to  regard  the 
narrow  longitudinal  area,  through  which  issue  the  anterior 
roots  of  the  spinal  nerves,  as  the  antero-lateral  fissure.    The 

(8)    Fissura  mediana  posterior.         (9)    Sulcus  lateralis  posterior. 


THE    SPINAL    CORD.  I65 

anterior  toots  do  not  emerge  in  line  one  above  another,  nor 
is  there  any  groove  on  the  surface  of  the  cord;  thus  the  so- 
called  fissure  cannot  be  exactly  located.  It  is  situated  op- 
posite the  anterior  cornu  of  gray  matter  and  in  line  with 
the  ventro-lateral  groove  of  the  medulla  oblongata.  It  sub- 
divides the  antero-lateral  surface  into  anterior  and  lateral 
surfaces. 

The  Postenor  Intermediate  Furrow^^  is  a  slight  longi- 
tudinal groove  which  subdivides  the  posterior  surface  into 
postero-median  surface  and  postero-lateral  surface.  From  it 
a  connective  tissue  septum  extends  into  the  cord  and  sepa- 
rates the  columns  of  Goll  and  Burdach  from  each  other.  The 
posterior  intermediate  furrow  is  found  only  in  the  upper 
part  of  the  cord,  in  the  cervical  and  dorsal  regions. 

The  spinal  cord  is  composed  of  (1)  GTray  matter,  in  the 
central  part;  and  (2)  White  matter,  in  the  peripheral  area. 
It  is  like  the  medulla  and  pons  in  having  the  white  matter 
on  the  surface. 

1.  Gray  Matter  of  the  Cord. 
A  column  of  gray  niatter,ii  crescentric  in  section,  extends 
throughi  the  center  of  each  lateral  half  of  the  spinal  cord. 
The  crescent  is  convex  medially;  and  is  joined  to  its  fellow, 
a  little  in  front  of  the  middle,  by  a  transverse  lamina  of  gray 
matter,  called  the  posterior  commissure}'^  It  is  joined  to 
the  white  matter  of  the  opposite  side  by  the  anterior  com- 
missure.^^ The  points  of  the  crescent  are  directed  forward 
and  backward,  respectively,  and  form  the  anterior  and  pos- 
terior cornua}"^     Together,  the  two  crescents  and  the  gra;y 

(10)  Sulcus  intermedius  posterior. 

(11)  Substantia  grisea 

(12)  Commissura  posterior  et  c.  anterior  grisea. 

(13)  Commissura  anterior  alba. 

(14)  Columnse  anteriores  and   c.  posteriores. 


l66  THE    BRAIN    AND    SPINAL    CORD 

commissure  form  an  H-shaped  column  of  gray  matter.  The 
H-shaped  column  is  well  marked  in  the  cervical  and  thoracic 
regions;  but,  toward  the  lower  end  of  the  cord,  the  crescents 
become  short  and  thick  and  the  gray  column  is  almost  cylin- 
drical. 

The  gray  matter  of  the  cord  is  of  two  kinds:  (1)  The 
substantia  gelatinosa  Eolandi,  which  forms  (a)  a  cap  for 
the  head  of  the  posterior  cornu  and  (b)  an  envelope  for  the 
central  canal,  or  ventricle,  of  the  cord.  (2)  The  substantia 
spongiosa.  The  latter  forms  all  the  H-shaped  column  except 
the  tips  of  the  posterior  horns  and  the  thick  sheath  of  the 
central  canal.  Imbedded  in  the  neuroglia,  there  is  a  network 
of  medullated  nerve  fibers,  running  longitudinally,  dorso- 
ventrally  and  transversely,  which  gives  it  a  spongy  appear- 
ance under  the  microscope. 

Gray  Crescent. — It  is  made  up  of  (1)  The  Anterior 
Cornu ;i^  (2)  The  Center,^^  which  is  joined  to  its  fellow  of 
the  opposite  side  by  the  gray  commissure;  and,  (3)  The  Pos- 
terior Cornu.i'''  There  is  a  lateral  projection  from  the  base 
of  the  anterior  cornu  in  the  cervical  and  upper  dorsal  region, 
called  the  lateral  horn}^  The  reticula,  or  processus  retic- 
ularis, forms  a  lateral  projection  from  the  base  of  the  pos- 
terior cornu.     It  is  found  in  the  cervical  region. 

(1)  The  Anterior  Cornu^^  is  short  and  thick  compared 
with  the  posterior  cornu.  It  is  thickest  in  the  cervical  and 
lumbar  enlargements;  in  the  mid- thoracic  region  it  is  more 
slender.  It  does  not  reach  the  surface  of  the  cord  as  does  the 
posterior  cornu.  It  ends  in  a  bulbous,  serrated  head,  which 
points  toward  the  antero-lateral  fissure.    From  it  the  anterior 

(15)  Columna  anterior. 

(16)  Substantia  intermedia  grisea. 

(17)  Columna  posterior. 

(18)  Columna  lateralis. 


THE    SPINAL    CORD.  167 

roots  of  the  spinal  nerves  rise;  and,  together  with  the  an*- 
terior  root-fihers,  it  separates  from  each  other  the  anterior 
and  lateral  white  colnmnsi^  of  the  cord. 

Cells. — The  anterior  cornu  contains  two  columns  of  large 
vesicular  eell-bodiesy^o  a  medial  and  a  lateral  column.  These 
columns  are  continuous  throughout  the  cord.  Their  axones 
compose  the  greater  part  of  all  anterior  roots  of  the  spinal 
nerves.  From  the  lateral  column,  and  from  a  part  of  the 
medial,  the  axones  enter  the  spinal  nerves  of  the  same  side; 
the  remainder  pass  through  the  anterior  (white)  commis- 
sure^i  to  the  opposite  nerves.  They  are  distributed  to  the 
muscles  of  the  trunk  and  extremities.  Those  neurones  whose 
centers  are  in  the  medial  column  are  believed  to  innervate 
the  dorsal  muscles  of  the  trunk.  The  muscles  of  the  ex- 
tremities are  innervated  by  th^  dorso^lateral  column;  the 
ventral  muscles  of  the  trunk,  by  the  ventro -lateral  column. 
In  the  cervical  region,  the  ventro-lateral  column  gives  origin 
to  the  phrenic  and  spinal  accessory  nerves  (Quain).  The 
end  tufts  of  the  pyramidal  fibers  and  of  the  descending 
cerebellar  fibers  are  in  relation  with  the  dendrities  or  bodies 
of  the  cells  of  the  anterior  cornu.  Fibers  from  the  pos- 
terior roots  of  the  spinal  nerves  and  from  cell-bodies  within 
the  cord,  likewise,  terminate  in  relation  with  them.  The 
cells  of  the  anterior  cornu  are  both  motor  and  trophic  ( ?). 

Lesions. — The  cells  in  the  anterior  cornu  are  the  seat  of 
hemorrhagic  inflammation  and  rapidly  degenerate  in  acute 
anterior  poliomyelitis:  in  progressive  museularr  atrophy  and 
in  amyotropljic  lateral  sclerosis  they  degenerate  slowly.  As 
a  result  of  the  first,  sudden  paralysis  occurs.  The  muscles 
waste  away  in  the  second  and  third  because  the  nerves  con- 

(19)  Funiculus  anterior  and  funiculus  lateralis. 

(20)  Perikaryons. 

(21)  Commissura  anterior  alba. 


l68  THE    BRAIN    AND    SPINAL    CORD. 

trolling  the  muscles  and  their  blood  supply  are  gradually 
destroyed.  In  the  last,  the  muscles  are  also  spastic,  because, 
as  we  shall  see  farther  on,  the  involvement  of  the  pyramidal 
tracts  cuts  off  cerebral  inhibition. 

(2)  The  Central  Part  of  the  Crescent^^  is  both  afferent 
and  efferent.  In  it  are  located  important  reflex  centers,  such 
as,  the  Cilio-spinal,  Secretory,  Yaso-motor,  Visceral,  Geni- 
tal, etc.  In  the  lumbar  enlargement  are  centers  of  defeca- 
tion, micturition,  erection,  ejaculation,  parturition;  in  the 
cervical  enlargement  the  cilio-spinal,  cardio-accelerator,  etc., 
are  found.  The  center  of  the  crescent  contains  three  columns 
of  cell-bodies:  The  intermedio-lateral  column  of  large  vesic- 
ular cell-bodies,23  situated  near  the  lateral  surface .  of  the 
crescent;  the  middle  column  (Waldeyer),  deep  in  the  cres- 
cent at  the  junction  of  the  gray  commissure;  and  the  dorsal 
column  of  Clark,^*  which  is  situated  near  the  inner  surface 
of  the  base  of  the  posterior  comu.  The  neurones  of  the 
central  part  of  the  crescent  axe  largely  sympathetic;  this 
is  especially  true  of  Clark's  column  and  to  less  extent  of  the 
intermedio-lateral  column. 

The  intermedio-lateral  column  is  best  marked  in  the 
thoracic  region ;  but  is  also  found  in  the  cervical  and  lumbar 
cord.  Its  cell-bodies,23  which  are  large  and  vesicular,  are  in 
relation  with  end-tufts  of  fibers  from  the  posterior  roots; 
and  they  give  rise  to  efferent  fibers  that  enter  the  anterior 
roots  of  the  spinal  nerves.  Those  fibers  are  probably  sympa- 
thetic and  supply  the  muscles  of  the  glandular  and  circu- 
latory systems  (Morris).  Other  axones  from  this  column 
enter  the  antero-lateral  ascending  cerebellar  tract. 

(22)  Substantia  intermedia  grisea. 

(23)  Perikaryons. 

(24)  Nucleus  dorsalis. 


THE    SPINAL    CORD.  169 

The  middle  column  (Waldeyer)  is  composed  of  mediiim- 
sized  neiirone-centers,23  which  are  most  abundant  in  the 
cervical  region,  where  this  column  is  best  shown.  Fibers 
from  the  posterior  spinal  roots  have  been  traced  into  the 
column  and  probably  the  cell-bodies  give  rise  to  some  of  the 
fiber-s  of  the  antero-lateral  ascending  cerebellar  tract.  But 
very  little  is  certainly  known  of  the  function  of  this  column. 

Clark's  column  (nucleus  dorsalis)  is  continuous  only 
through  the  thoracic  region;  but  it  is  represented  by  the 
nuclei  of  Stilling  in  the  cervical  and  lumbar  regions  and, 
in  the  medulla  oblongata.,  by  the  accessory  cuneate  nucleus. 
Clark's  cells  are  in  relation  with  the  end-tufts  of  fibers  from 
the  posterior  roots  of  the  spinal  nerves.  The  axones  of 
Clark's  cells  form  the  direct  cerebellar  tract,  and  help  to 
form  the  anterior  roots  of  the  spinal  nerves.  The  latter  are 
sympathetic  fibers,  anabolic  and  inhibitory  in  function. 
They  are  distributed  to  the  blood  vessels,  glands  and  muscu- 
lar coat  of  the  alimentary  canal  (Morris). 

(3)  The  Posterior  CornuJ^^  except  in  the  lumbar  cord, 
is  slender.  It  is  longer  than  the  anterior  cornu  and  reaches 
the  surface  in  the  postero-lateral  fissure,  where  it  receives 
the  posterior  roots  of  the  spinal  nerves.  The  posterior  cornu 
presents  a  slight  enlargement  near  its  extremity^  called  the 
caput  cornuj^^  which  tapers  off  to  the  apex  cornu.^'^  The 
head  is  joined  to  the  base  of  the  horn  by  a  constricted  part, 
the  cervix.^^  The  head  of  the  posterior  horn  is  capped  by 
the  substantia  cinerea  gelatinosa  of  Rolando.  The  posterior 
corpu  separates  the  posterior^^  from  the  lateral  column^^  of 
the  cord. 

The  cells  of  the  posterior  cornu  are  very  numerous.     They 

(25)  drolumna  posterior,  (28)    Cervix  columhge  posterioris. 

(26)  Caput  columnae   posterioris.      (29)    Funiculus  posterior. 

(27)  Apex  columnse  po&terioris.        (30)    Funiculus  lateralis. 


I/O  THE    BRAIN    AND    SPINAL    CORD. 

have  smaller  bodies  than  the  cells  of  the  anterior  cornu  and 
are  less  definitely  grouped.  In  function  they  are  afferent  and 
associative.  They  are  classified  as  follows:  (a)  The  periph- 
eral cells,  having  a  body  and  one  long  process,  the  comet  cells 
(Waldeyer) ;  (b)  the  central  cells;  (c)  the  basal  cells; 
(d)  the  cells  of  the  substantia  gelatinosa,  which  have  small 
and  round  bodies  (Gierke  and  H.  Yirchow) ;  and  (e)  the 
solitary,  fusiform-bodied  cells,  scattered  throughout  the  pos- 
terior horn.  The  dendritic  processes  of  the  cells  of  the  pos- 
terior cornu  probably  ramify  in  the  gray  matter  adjacent  to 
them.  The  axones  run  in  various  directions,  viz.,  into  the 
ground  bundles,  forming  the  septomarginal  and  cornu  com- 
missural tracts,  and,  perhaps,  the  comma  tract;  into  Bur- 
dach's  column;  into  the  center  and  anterior  cornu  of  the 
same  side;  and,  very  largely,  into  the  gray  crescent  of  the 
opposite  side.  These  last  fibers,  together  with  the  antero- 
lateral ascending  cerebellar  tract,  account  largely  for  the 
immediate  crossing  of  the  main  sensory  path.  Many  fibers 
from  the  posterior  roots  of  the  spinal  nerves  terminate  in 
ramifications  about  the  cells  of  the  posterior  cornu  on  both 
sides,  viz. :  Those  axones,  forming  the  lateral  group  of  small 
fibers  in  the  posterior  roots  of  the  spinal  nerves,  end  in 
relation  with  the  small,  round  cell-bodies  in  the  substantia 
gelatinosa  Rolandi;  other  fibers  end  about  the  peripheral, 
the  central,  the  basal  and  the  solitary  cell-bodies. 

The  Posterior,  or  Gray,  Commissure^^  completes  the  gray 
matter  of  the  cord.  It  unites  the  two  gray  crescents  together 
a  little  in  front  of  their  center,  except  in  the  lumbar  region 
where  it  joins  their  centers.  It  forms  the  fioor  of  the  pos- 
terior median  fissure ;  and,  in  front,  is  in  relation  with  the 
white  commissure.     It  is  pierced  longitudinally  by  Hie  cen^ 

(31)    Cotnmlssura  anterior  grlsea,  and  c.  posterior. 


THE    SPINAL    CORD.  I7I 

tral  canal  of  the  spinal  cord,  around  which  is  a  thick  en- 
velope of  substantia  gelatinosa.  That  part  of  the  commissure 
in  front  of  the  canal  and  that  behind  it  are  frequently 
described  as  the  anterior  and  posterior  gray  commissures. 
The  posterior  commissure  is  composed  of  neuroglia  in  which 
are  imbedded  the  bodies  of  many  nerve  cells  and  a  large 
number  of  medullated  fibers.  The  medullated  fibers  are  de- 
rived from  the  posterior  roots  of  the  spinal  nerves,  and  from 
intrinsic  neurones  of  the  cord,  whose  centers  are  situated 
chiefly  in  the  commissure  and  in  the  posterior  cornu.  The 
commissure  contains  a  long  sensory  tract  between  the  ven- 
tricle and  dorsal  surface  (Ciaglinski).  The  long  sensory 
tract  is  found  in  the  thoracic  portion  of  the  cord  and  the 
discoverer  believes  it  to  be  made  up  of  ascending  root-fibers 
which  conduct  pain  and  temperature  impulses.  It  is  in  need 
of  further  investigation. 

2.    White  Matter  of  the  Coed. 

The  white  matter^^  ^f  ii^q  spinal  cord  is  disposed  in  its 
peripheral  area  and  in  the  anterior  commissure.^^  It  is  com- 
posed of  medullated  nerve  fibers  (axones  and  collaterals) 
imbedded  in  a  small  amount  of  neuroglia;  and,  like  the 
gray  matter,  it  is  richly  supplied  with  blood  vessels.  It  is 
also  supported  by  a  connective  tissue  network  derived  from 
the  pia  mater.  The  fibers  run  transversely,  dor so-ventr ally 
and  longitudinally. 

Transverse  fibers  are  found  running  between  the  longi- 
tudinal columns  and  the  gray  matter,  or  vice  versa,  and  are 
continuous  with  the  longitudinal  fibers.  The  most  definite 
lamina  of  transverse  fibers  is  the  anterior  commissure. 

The  Anterior,  or  White,  Commissure. — It  connects  the  an- 

(32)  Substantia  alba. 

(33)  Commissura  anterior  alba. 


\y 


172  THE    BRAIN    AND    SPINAL    CORD. 

terior  and  lateral  white  columns  of  the  cord  with  the  op- 
posite gray  crescent.  It  is  located  in  front  of  the  gray 
commissure,  and  forms  the  floor  of  the  anterior  median  fis- 
sure. It  is  composed  of  medullated  fibers  belonging  to  (a) 
the  direct  pyramidal  tract,  (b)  the  antero-lateral  ground 
bundle,  (c)  the  antero-lateral  ascending  cerebellar  tract,  and 
(d)  of  the  crossed  fibers  to  the  anterior  roots  of  the  spinal 
nerves. 

The  dorso-ventral  fibers  of  the  spinal  cord  are  those  of 
the  anterior  roots  of  the  spinal  nerves,  in  their  course  from 
the  gray  matter  to  the  surface  of  the  cord;  and  of  the  pos- 
terior roots,  running  from  the  postero-lateral  fissure  to  their 
destination  in  the  gray  matter. 

The  Longitudinal  Fibers  comprise  most  of  the  white  matter 
in  the  cord,  forming  the  funiculus  anterior,  funiculus  later- 
alis and  funiculus  posterior.  They  are  disposed  around  the 
gray  crescent  in  bundles  or  tracts.  The  tracts  are  not  visible 
to  the  naked  eye,  nor  under  the  microscope  in  a  healthy  adult 
cord;  they  have  been  located  by  embryological,  experimental 
and  pathological  investigations.  The  longitudinal  fibers  rise 
in  the  brain,  in  the  spinal  cord  and  in  the  spinal  ganglia; 
some  run  upward  and  others  downward,  constituting  the 
tracts  of  the  cord.  Thus  the  tracts  are  characterized  as 
ascending,  descending  and  mixed  tracts. 

Ascending  Tracts:  (1)  Antero-lateral  ascending  cere- 
bellar tract,  (2)  Direct  cerebellar  tract,  (3)  Postero-lateral 
tract,  (4)  Postero-median  tract,  (5)  Marginal  tract  of  Lis- 
sauer,  (6)  Posterior  longitudinal  bundle,  (7)  Olivary  bundle 
(Hel wig's),  and  (8)  Ciaglinski^s  long  sensory  tract,  in  the 
gray  commissure. 

Descending  Tracts:  (1)  Uncrossed  (direct)  pyramidal 
tract,  (2)  Crossed  pyramidal  tract,  (3)  Antero-lateral  de- 
scending cerebellar  tract,  (4)   Comma  tract,  (5)   Septomar- 


THE    SPINAL    CORD.  173 

oinal  tract;  (6)  Cornu  commissural  tract,  (7)  Anterior 
longitudinal  bundle,  and  (8)  Crossed  descending  tract  of 
the  red  nucleus. 

Mixed,  Ascending  and  Descending,  Tract. — The  Antero- 
lateral ground  bundle. 

The  Large  Tracts  of  the  Antero-lateral  Columns^  of  the 
spinal  cord  are  seven  in  number,  viz.,  the  antero-lateral 
ground  bundle,  two  pyramidal  tracts,  three  cerebellar  tracts 
and  the  marginal  bundle  of  Lissauer. 

The  antero-lateral  ground  bundle^^  occupies  the  deep  part 
of  the  column.  It  embraces  the  anterior  cornu  of  gray  mat- 
ter and  covers  the  outer  surface  of  the  center  of  the  crescent 
and  the  base  of  the  posterior  cornu.  It  approaches,  but  does 
not  quite  reach,  the  surface  of  the  cord.  It  is  separated  from 
the  anterior  median  fissure  by  the  uncrossed  (direct)  pyram- 
idal tract;  the  antero-lateral  descending  and  ascending 
cerebellar  tracts  run  between  it  and  the  surface  of  the  cord; 
and,  behind,  it  is  in  relation  with  the  crossed  pyramidal  tract. 
The  antero-lateral  ground  bundle  is  composed  of  ascending 
and  descending  fibers.  It  is  a  short  fiber  tract,  associative 
and  commissural  in  function.  That  part  situated  in  the 
anterior  column  is  largely  commissural,  between  the  anterior 
cornua;  while  the  part  in  the  lateral  column  is  chiefly  asso- 
ciative, and  connects  different  segments  of  the  cord  on  the 
same  side.  The  antero-lateral  ground  bundle  is  continued 
in  the  formatio  reticularis  of  the  medulla,  pons  and  mid- 
brain, constituting  a  short  fiber  tract  which  extends  from  the 
lower  part  of  the  cord  to  the  basal  ganglia  of  the  cerebrum- 
Some  of  its  ascending  fibers  form  the  posterior  longitudinal 
hundle,^^  and  extend  up  to  the  motor  cranial  nuclei  and 

(34)  Funiculus  antero-lateralis.  , 

(35)  Fasciculus  proprius  antero-lateralis. 

(36)  Fasciculus  longitudinalis  medialls. 


174  THE    BRAIN    AND    SPINAL    CORD. 

hypothalamic  region.  Imbedded  in  the  tract,  also,  between 
the  anterior  and  lateral  areas,  is  seen  the  anterior  longitu- 
dinal hundle^'^  as  far  as  lumbar  cord  (Barker).  The  latter 
runs  from  the  superior  quadrigeminal  body  to  the  cilio-spinal 
and  other  centers. 

The  uncrossed  (direct)  pyramidal  tract  (Turck^s  col- 
umn) ^^  occupies  a  thin  area  next  the  anterior  median  fissure. 
It  is  a  continuation  of  the  same  tract  in  the  medulla.  Its 
fibers  are  axones  of  cortical  cells  whose  bodies  are  situated  in 
the  Eolandic  region  of  the  cerebrum.  "  As  the  tract  descends 
in  the  cord,  the  fibers  decussate  through  the  anterior  commis- 
sure, and  terminate  in  relation  with  the  cells  of  the  opposite 
anterior  cornu.     (N.  15,  Add.) 

The  antero-lateral  descending  cerebellar  tract  (Marchi 
and  Loewenthal's  column), ^^  together  with  the  ascending 
antero-lateral  cerebellar  tract,  occupies  a  thin  peripheral  area, 
broadest  posteriorly,  which  extends  from  the  direct  pyramidal 
teact  outward  and  backward,  over  the  antero-lateral  ground 
bundle,  to  the  middle  of  the  lateral  surface  of  the  cord.  Its 
posterior  border  is  in  relation  with  the  direct  cerebellar  tract 
and  the  crossed  pyramidal  tract.  The  fibers  of  the  two  tracts 
are  mingled  together;  but  the  descending  fibers  are  found, 
chiefiy,  in  the  anterior  part  of  the  common  area  and  the 
ascending  in  the  posterior  part.  The  descending  fibers  are 
axones  from  the  cortical  cells  (Purkinje's)  of  the  cerebellum. 
They  descend  to  the  spinal  cord  through  the  inferior  cere- 
bellar peduncle  and  the  lateral  area  of  the  medulla  and, 
probably,  end  in  the  anterior  cornu  of  gray  matter.  The 
descending  cerebellar  tract  forms  one  segment  of  an  indirect 
motor  path  (N.  11,  Add,). 

(37)  Fasciculus  ventralis. 

(38)  Fasciculus  cerebro-spinalis  anterior. 

(39)  Fascicularis    antero-lateralis    superficlaHs    (descettdens-ascen- 
dens). 


THE    SPINAL    CORD.  175 

Antero-lateral  ascending  cerebellar  tract  (Column  of 
Gowers).^^ — It  is  found  chiefly  in  the  posterior  part  of  the 
area  common  to  it  and  the  descending  tract.  It  is  composed 
of  axoriic  processes  of  cells  whose  bodies  are  situated  in  the 
center  of  the  crescent  and  base  of  the  anterior  comu,  chiefly 
on  the  opposite  side  of  the  cord  (v.  Lenhossek).  Most  of  the 
fibers  of  the  antero-lateral  ascending  cerebellar  tract  cross 
near  their  origin  through  the  anterior  commissure  of  the  cord. 
In  the  medulla,,  the  tract  ascends  through  the  dorsal  part  of 
the  lateral  area,  sending  collaterals  to  the  lateral  nucleus ; 
it  then  continues,  through  the  formatio  reticularis  of  the 
pons,  to  a  point  near  th^- inferior  quadrigeminal  body,  where 
it  is  bent  backward  over  the  superior '  cerebellar  peduncle, 
and  enters  the  vermis  cerebelli  superior  through  the  valve  of 
Vieussens  (Hoche).  According  to  Mott,  two  small  bundles 
leave  this  tract  at  the  angle,  and  run  near  the  lateral  fiilet 
to  the  superior  corpus  quadrigeminum  and  optic  thalamus. 
Gowers'  tract  -  carries  thermic  and  pathetic  impulses.  The 
olivary  bundle  of  the  cord,  the  triangular  tract  of  Helwig, 
is  found  near  the  middle  of  the  area  common  to  the  antero- 
lateral cerebellar  tracts ;  it  may  be  traced  to  the  lumbar 
region,  where  its  longest  fibers  rise.  It  ends  in  the  olive  of 
the  medulla  oblongata  and  is  afferent  in  conduction. 

The  direct  cerebellar  tract  (dorso-lateral  cerebellar 
tract) ^^  runs  posterior  to  the  antero-lateral  tracts.  It  is 
superfitially  located,  and  extends  from  the  middle  of  the 
lateral  surface  of  the  cord  back  to  the  postero-lateral  fissure, 
except  in  the  lumbar  cord.  There  its  absence  allows  the 
crossed  pyramidal  tract  to  come  to  the  surface.  The  direct 
cerebellar  tract  terminates  in  the  superior  worm  of  the  cere- 
bellum.    In  the  medulla,  it  forms  a  part  of  the  restiform 

(40)    Fasciculus  cerebello-splnalU. 


176  THE    BRAIN   AND    SPINAL    CORD. 

body.  Its  fibers  are  axones  of  Clark's  vesicular  cells.  Th&y 
convey  impulses  of  equilibrium  received,  especially,  from  the 
viscera. 

The  crossed  pyramidal  tract^^  forms  a  considerable  part 
of  the  lateral  column  of  the  spinal  cord.  It  is  covered, 
superficially,  by  the  cerebellar  tracts  in  the  cervical  and 
dorsal  cord;  but  in  the  lumbar  cord,  it  forms  part  of  the 
surface.  Its  deep  surface  is  in  relation  with  the  posterior 
comu  of  gray  matter,  the  antero-lateral  ground  bundle  and 
marginal  bundle  of  Lissauer.  The  fibers  composing  it  are 
axones  of  cell-bodies  in  the  Rolandic  region  of  the  cerebral 
cortex.  They  rise  with  those  of  the  uncrossed  (direct)  pyram- 
idal tract  ;^2  ^nd  the  two  run  as  one  tract  down  through 
the  genu  and  anterior  two-thirds  of  the  posterior  segment  of 
the  internal  capsule,  the  middle  three-fifths  of  the  crusta,  the 
ventral  longitudinal  fibers  of  the  pons  and  the  pyramid  of 
the  medulla.  In  the  medulla  the  two  tracts  separate.  The 
crossed  tract  decussates  with  its  fellow  through  the  anterior 
median  fissure,  pierces  the  anterior  gray  cotnu  and  descends 
in  the  lateral  column  of  the  cord.  It  terminates  in  relation 
with  the  cell-bodies  of  the  anterior  comu.  The  uncrossed 
tract  follows  the  anterior  median  fissure  as  already  described. 
Both  end  chiefly  in  the  anterior  gray  comu  opposite  to  their 
cortical  origin.  According  to  Marchi,  about  twenty  per  cent 
of  the  fibers  remain  uncrossed.  The  pyramidal  tracts  are 
the  cerebral  motor  tracts.  By  them  motor  and  inhibitory 
impulses  are  carried  to  the  cord.  In  the  dorso-lateral,  part 
■of  the  crossed  pyramidal  area  is  found  the  crossed  descending 
tract  of  the  red  nucleus.  It  extends  as  far  as  the  first  lumbar 
segment  and  ends  in  the  center  of  the  gray  crescent.  It  is 
efferent  in  function.     (N".  15,  Add.) 

(41)    Fasciculus  cerebro-splnalis  lateralis. 
(A2)    Fasciculus  cerebro-spinalis  anterior. 


THE    SPINAL    CORD.  1/7 

Lesions. — The  pyramidal  tracts  (especially  the  crossed)  are 
involved  in  lateral  sclerosis  and  in  amyotrophic  lateral  sclero- 
sis ;  and,  as  a  consequence  of  it,  both  voluntary  and  inhibitory 
impulses  from  the  brain  are  interfered  with,  hence  the  spastic 
paralysis  and  exaggerated  reflexes.  The  pyramidal  tract  may 
be  more  or  less  involved  in  insular  sclerosis  and  in  bulbar 
paralysis,  and  the  symptoms  vary  with  the  amount  of 
sclerosis.  Gliosis  of  the  pyramidal  and  cerebellar  tracts  and 
the  posterior  tracts  (Dejerine  and  Letulle)  has  been  demon- 
strated in  Friedrich's  hereditary  ataxia,  and  the  involvement 
of  the  pyramidal  tracts  explains  the  spastic  paralysis  which 
affects  both  the  arms  and  legs.  In  ataxic  paraplegia 
(Gowers)  there  is  diffuse  sclerosis  of  the  lateral  and  posterior 
columjis  of  the  cord.  It  is  the  degeneration  in  the  pyramidal 
tracts  that  causes  the  spastic  gait,  incoordinated  arm  move- 
ments and  early  increase  of  the  reflexes,  observed  in  that 
affection. 

The  marginal  tract  of  Lissaiier*^  is  a  small  tract  com- 
posed of  ascending  branches  of  the  outer  set  of  fibers  in  the 
posterior  roots  of  the  spinal  nerves.  It  is  situated  on  the 
lateral  surface  and  apex  of  the  posterior  cornu.  Its  fibers, 
after  ascending  a  short  distance,  end  about  the  cell-bodies  of 
the  substantia  gelatinosa  Rolandi. 

Tracts  of  the  Posterior  Column  of  the  Cord.^* — There  are 
three  tracts  in  this  column,  viz.,  the  postero-lateral,  the 
postero-median  and  the  ground  bundle,  or  fasciculus  pro- 
prius,  which  may  be  divided  into  the  comma  tract,  septo- 
marginal tract  and  cornu  commissural  tract.  The  last  three 
are  descending  tracts. 

Postero-lateral  tract  (Burdach's  column)  .^s — It  runs  up- 
ward just  medial  to  the  posterior  cornu  of  gray  matter.    It  is 

(43)  Fasciculus   marginalis.  (45)    Fasciculus  cuneatus. 

(44)  Funiculus  pasterior. 


178  THE    BRAIN   AND    SPINAL    CORD. 

made  up  of  ascending  branches  of  the  posterior  roots  of  the 
spinal  nerves  and  of  intrinsic  fibers  whose  cell-bodies  are  in 
the  gray  matter  of  the  cord.  It  become^  the  fasciculus  cunea- 
tus  and  fasciculus  Rolandi,  in  the  medulla;  and  it  ends 
chiefly  in  the  cuneate  and  Eolandic  nuclei.  A  certain  number 
of  its  fibers  are  continued  directly  into  the  interolivary  fillet 
and  others  into  the  arciform  fibers  without  interruption ;  and 
some  of  the  fibers  of  Burdach's  column  end  in  the  gray 
matter  of  the  cord  as  they  ascend.  In  the  midst  of  the 
postero-lateral  tract,  in  the  cervical  and  upper  thoracic  cord, 
is  a  small  bundle  of  descending  fibers,  the  comma  tract;  in 
the  lumbar  and  sacral  segments  are  found  two  descending 
tracts,  the  septomarginal  and  the  cornu  commissural.  The 
two  latter  tracts  are  entirely  intrinsic,  and  there  seems  to  be 
no  doubt  that  the  comma  tract  is  in  part  so,  as  some  of  its 
fibers  degenerate  after  section  either  of  the  posterior  roots  of 
the  spinal  nerves  or  destruction  of  the  posterior  horn  of  gray 
matter.  Burdach's  column  conveys  all  kinds  of  common 
sensory  impulses  (N.  13,  Add.). 

The  Cornu  Commissural  Tract  is  placed  between  the  pos- 
terior cornu,  the  gray  commissure  and  posterior  septum.  It 
extends  up   to  the   eleventh  thoracic   aegment. 

Septomarginal  Tract  (Bruce  and  Muir). — ^This  tract  is 
a  semi-oval  tract  next  the  posterior  septum  in  the  third 
lumbar  segment  (Flechsig)  ;  and  a  triangular  tract  bounded 
by  the  septum  and  dorsal  surface  of  the  cord  in  the  fifth 
sacral  segment  (triangle  median,  Gombault  and  Phillipe). 

The  Comma  Tract. — It  is  conuna-shaped  in  section,  the 
head  being  directed  forward.  It  is  composed  of  descending 
branches  of  the  posterior  roots  of  the  spinal  nerves,  and  of 
intrinsic  fibers  of  the  spinal  cord.  It  is  considerably  inter- 
mingled with  fibers  of  the  postero-lateral  tract,  and  its 
termination  is  in  the  posterior  cornu  of  the  cord. 


THE    SPINAL    CORD.  1/9 

The  postero-median  tract  (GolFs  column)  ^^  ascends  be- 
tween the  postero-lateral  tract  and  the  posterior  median 
septum.  Like  the  postero-lateral  tract  in  the  cervical  region, 
it  extends  in  depth  ventrally  to  the  gray  commissure.  It  is 
composed  of  ascending  branches  of  the  posterior  roots  of  the 
spinal  nerves.  Continued  into  the  medulla  oblongata,  the 
postero-median  tract  becomes  the  fasciculus  gracilis.  It  ter- 
minates at  the  clava,  the  fibers  ending  in  relation  with  the 
cell-bodies  of  the  nucleus  gracilis.  A  number  of  fibers, 
diverging  from  the  tract,  end  in  the  gray  matter  of  the  spinal 
cord,  and  a  few,  without  interruption,  continue  in  the  inter- 
olivary  fillet  to  the  thalamus  and  in  the  arciform'  fibers  of 
the  medulla  to  the  cerebellnm.  GoU's  column  carries  im- 
pulses of  the  muscular  sense,  and  is  particularly  involved  in 
locomotor  ataxia.  AH  varieties  of  impulses,  of  bodily  sensa- 
tion are  carried  by  Bur  dachas  column. 

Lesions  in  the  posterior  colunm®  cause  disturbances  of 
sensation,  loss  of  reflexes  and  impaired  equilibration.  These 
columns  are  usually  involved,  by  extensions  from  the  pos- 
terior roots,  in  loeomotor  ataxia  (posterior  sclerosis),  hence 
the  parsesthesia,  crises,  loss  of  reflexes,  contracted  pupil,  dis- 
turbed equilibrium  and  ataxic  gait.  •  They  may  be  involved 
in  insular  sclerosis,  and  the  sensory  symptoms  depend  upon 
the  extent  of  their  degeneration.  Section  of  the  posterior 
column  on  one  side  in  any  segment  of  the  spinal  cord  pro- 
duces, on  the  same  side,  more  or  less  loss  of  sensation  in  that 
part  of  the  body  supplied  by  the  segment  cut,  and,  on  the 
opposite  side,  complete  anaesthesia  below  the  section. 

ROOTS   OF   THE   SPINAL   NERVES. 

Thirty-one  pairs  of  spinal  nerves  rise  from  the  side  of  the 
cord.     Each  nerve  has  two  roots:    an  anterior,  efferent  or 

(46)    Fasciculus  gracilis. 


l80  THE    BRAIN    AND    SPINAL    CORD. 

motor,  root  and  a  posterior,  afferent  or  sensory,  root.  These 
roots  descend  more  or  less  from  their  origin  to  the  inter- 
vertebral foramen  in  which  they  unite  to  form  the  spinal 
nerve.  The  roots  of  the  first  cervical  nerve  are  horizontal; 
those  of  the  first  dorsal  nerve  descend  the  width  of  two  ver- 
tebras, and  those  of  the  twelfth  dorsal,  the  width  of  four 
vertebrae;  while  the  roots  of  the  coccygeal  nerve  extend  from 
the  first  lumbar  vertebra  to  the  second  piece  of  the  coccyx, 
through  ten  vertebrae. 

Anterior  Root. — In  all  spinal  nerves,  except  the  first,  the 
anterior  root"^^  is  smaller  than  the  posterior.*^  It  is  com- 
posed of  from  four  to  six  fasciculi,  which  soon  combine  into 
two  bundles.  After  piercing  the  dura  mater,  the  anterior 
root  unites  with  the  posterior,  beyond  the  latter's  ganglion, 
and  forni'S  a  spinal  nerve.    It  is  efferent,  or  motor,  in  function. 

Super ficml  (apparent)  Origin. — The  anterior  root  is  com- 
posed of  medullated  axones  which  issue  from  the  narrow 
longitudinal  area  commonly  called  the  Antero-lateral  Fissure. 

Deep  (real)  Origin. — The  medullated  axones  rise  from  the 
Medial,  Lateral,  Clark's  and  Intermedio-lateral  columns  of 
cell-bodies  on  the  same  side,  and  from  the  Medial  column  of 
the  opposite  side. 

Lesions. — The  lower  motor  neurones  (spinal  and  cranial) 
are  probably  in  a  state  of  toxic  irritation  in  laryngismus 
stridulus,  tetanus,  acute  ascending  paralysis  (Landry), 
strychnine  poisoning,  etc.,  hence  the  twitchings,  spasms  and 
convulsions.  In  spinal  meningitis  both  the  anterior  and 
posterior  roots  are  affected. 

The  posterior  root^^  is  the  sensory,  or  afferent,  root.  It 
is  larger  than  the  anterior  root,  except  in  the  case  of  the  first 
cervical  nerve;    and  is  composed  of  from  six  to  eight  fas- 

(47)  Radix  anterior.  (49)    Radix   posterior. 

(48)  Radix  posterior. 


THE    SPINAL    CORD.  l8l 

ciculi^  which  also  combine  at  once  into  two  bundles.  The 
posterior  root  pierces  the  dura  mater  separately.  It  unites 
with  the  anterior  root  in  the  intervertebral  foramen.  Near 
the  outer  end,  it  presents  a  swelling  which  contains  large 
vesicular-bodied  nerve  cells,  and  is  called  a  spinal  ganglion.^^ 
(It  is  occasionally  absent  on  the  first  nerve.)  The  posterior 
root,  external  to  the  ganglion,  is  made  up  of  the  dendritic 
processes  (Cajal)  of  the  ganglion  cells.  These  dendrites  ex- 
tend to  the  most  distant  parts  of  the  body;  they  are  the 
sensory  fibers  of  the  spinal  nerves.  Internal  to  the  ganglion, 
the  posterior  root  is  composed  of  axones,  which  rise  from  the 
ganglion  cells.  Both  the  axonic  and  dendritic  processes  are 
medullated. 

Superficial  Origin  (apparent  central  termination). — The 
posterior  roots  of  the  spinal  nerves  enter  the  Postero-lateral 
Fissure ;  and,  at  once,  divide  into  an  outer  set  of  small  fibers 
and  an  inner  set  of  large  fibers  with  some  small  ones  inter- 
spersed. The  fibers  of  each  set  bifurcate  into  a  large 
ascending  and  a  small  descending  branch.  Collaterals  rise 
from  the  parent  axone  and  from  both  branches. 

Deep  Origin  (real  central  termination). — The  ascending 
divisions  of  the  outer  set  of  fibers  run  a  short  distance  along 
the  external  surface  of  the  posterior  cornu,  and  end  in 
ramifications  about  the  cell-bodies  of  the  Substantia  Gela- 
tinosa  Rolandi.  They  form  the  tract  of  Lissauer.  The  ascend- 
ing divisions  and  collaterals  of  the  inner  set  of  fibers  from 
the  posterior  root  run  (1)  To  the  Gray  Matter  of  the  Cord, 
viz. :  To  all  parts  of  the  Posterior  Cornu,  to  the  Center  of  the 
Crescent,  and  to  the  Anterior  Cornu  on  the  same  side,  and, 
through  the  gray  commissure,  to  the  Center  and  Cornua 
of  the  opposite  crescent.     Those  fibers  end  in  relation  with 

(50)    Ganglion  spinale. 


l82  THE    BRAIN   AND    SPINAL    CORD. 

the  dendrites  or  cell-bodies  situated  in  those  several  regions. 
(2)  To  the  Brain.  Of  the  ascending  fibers  from  the  posterior 
roots  of  the  spinal  nerves,  the  remainder  form  the  column 
of  Goll  and  most  of  Burdach's  column  and  ascend  to  the 
Gracile,  Cuneate  and  Rolandic  nuclei  of  the  medulla  oblon- 
gata. The  greater  number  terminate  in  those  nuclei,  but  a 
few  continue,  through  the  external  arciform  fibers,  to  the 
Vermis  Cerebelli  Superior,  and,  through  the  interolivary  fil- 
let, to  the  Cerebrum. 

The  descending  branches  of  the  posterior  root-fibers  have 
a  short  course.  They  end  in  the  gray  matter  of  the  cord. 
According  to  Mott  some  of  them  enter  into  the  comma  tract. 
They  are  not  well  understood. 

Lesion. — ^The  posterior  roots  of  the  spinal  nerves  are  first 
affected  (Obersteiner  and  Redlich)  in  locomotor  ataxia,  and 
the  lesion  extends  to  the  spinal  ganglia  (often)  and  to  the 
posterior  columns  of  the  cord. 

BLOOD   SUPPLY   OF   THE    SPINAL    CORD. 

The  vessels  supplying  the  cord  are  the  anterior  spinal 
artery^i  and  the  two  posterior  spinal  arteries,^^  which  rise 
at  the  foramen  magnum  from  the  vertebral  arteries,  and  are 
reinforced  by  cervical,  intercostal  and  lumbar  arteries.  The 
anterior  spinal  artery  descends  along  the  entrance  to  the 
anterior  median  fissure;  it  is  formed  by  the  union  of  two 
vessels,  one  from  each  vertebral.  The  posterior  spinal  artery, 
of  either  side,  is  in  reality  a  pair  of  vessels  which  freely 
communicate,  and  are  so  placed  as  to  embrace  the  posterior 
nerve  roots.  The  larger  vessel  of  the  pair  is  external  to  the 
nerve  roots,  while  the  smaller  is  between  them  and  the  pos- 

(51)  Arteria  spinalis  anterior. 

(52)  Arterise  spinales  posteriores. 


THE    SPINAL    CORD.  I83 

terior  median  fissure.  The  spinal  arteries  give  origin  to  two 
sets  of  branches,  namely,  the  centrifugal  and  centripetal 
arteries.  Both  sets  are  end-axteries  and  form  rich  longitu- 
dinal plexuses,  which  overlap  each  other  but  do  not  anas- 
tamose. 

The  Centrifugal  Arteries  rise,  first  and  chiefly,  from  the 
anterior  spinal  artery.  These  enter  the  anterior  median 
fissure  and,  running  lateralward,  supply  the  greater  part  of 
the  gray  matter.  Second,  a  few  centrifugal  arteries  rise 
from  the  posterior  spinal  arteries.  Running  into  the  pos- 
terior fissure,  they  are  distributed  to  the  posterior  white 
columns,  the  posterior  commissure  and  to  Clark's  column  of 
cells. 

The  Centripetal  Arteries  rise  from  both  the  anterior  and 
posterior  spinal  arteries.  They  enter  the  cord  at  right  angles 
to  the  surface,  and  supply  the  white  matter  and  the  peripheral 
parts  of  the  gray  substance,  including  the  tips  of  the  comua. 
Those  branches  to  the  comua  accompany  the  root-fibers. 

Veins. — The  veins^^  ^j^^t  carry  the  blood  from  the  interior 
of  the  cord  are  the  fissural  veins,  which  issue  from  the  fissures, 
the  root-veins,  which  accompany  the  anterior  and  posterior 
root-fibers  to  the  surface  of  the  cord,  and  a  small  number 
of  veins  that  issue  from  other  parts  of  the  surface  of  the 
spinal  cord.  All  unite  in  forming  the  Medulli-spinal 
Plexus,^^  spread  over  the  entire  surface  of  the  cord  beneath 
the  arachnoid  membrane.  In  the  upper  cervical  region,  the 
plexus  forms  two  or  three  ^mall  veins  which  empty  into  the 
vertebral  or  inferior  cerebellar  veins ;  elsewhere,  by  a  branch 
along  each  spinal  nerve,  the  plexus  communicates  with  the 


(53)  Venae. 

(54)  Venae  spinales  externse. 


l84  THE    BRAIN    AND    SPINAL    CORD. 

Meningo-rachidian  Veins,^^  outside  the  dura  mater,  and  is 
drained  into  the  vertebral,  intercostal,  lumbar  and  sacral 
veins.    No  valves  are  found  in  the  spinal  veins. 

Lymphatics. — Perivascular  and  perineural  spaces  carry 
the  lymph  from  the  spinal  cord.  There  are  no  lymphatic 
vessels  in  the  cord. 

(55)    Plexus   venosi   vertebrales   interni. 


CHAPTER  X. 


TRACING  OP  IMPULSES. 

Having  studied  the  grouping  and  chaining  together  of 
neurones,  let  us  now  make  the  knowledge  practical  by  tracing 
impulses  through  the  better  known  paths  formed  by  these 
various  neurone  groups.  The  paths  thus  formed  are  of  three 
kinds,  namely:  I.  Efferent,  or  motor;  II.  Afferent,  or 
sensory — ^General  and  Special  sense;    and  III.  Reflex. 

I.     Efferent,  or  Motor,  Paths. 

The  Pyramidal  Paths  are  direct,  as  they  do  not  pass 
through  the  cerebellum.  Their  impulses  ultimately  run  either 
through  the  spinal  or  the  cranial  nerves,  and  are  both  motor 
and  inhibitory.  Hence  the  increased  reflexes  and  spastic  con- 
tractions of  lateral  sclerosis. 

1.  Through  the  Spinal  Nerves. — Starting  in  the  upper 
three-fourths  of  the  Rolandic  area  of  the  cerebral  cortex,, 
motor  and  inhibitory  impulses  run  down  through  the  corona 
radiata,  the  anterior  two-thirds  of  the  posterior  segment  of 
the  internal  capsule,  the  middle  three-fifths  of  the  crusta, 
the  ventral  longitudinal  fibers  of  the  pons,  and  the  pjrramid 
of  the  medulla  oblongata,  whence  they  proceed  either  by  the 
crossed  or  uncrossed  (direct)  pyramidal  tract  to  the  anterior 
gray  cornu  in  the  opposite  side  of  the  spinal  cord.  By  the 
former  route,  the  impulses  cross  over  in  the  medulla,  through 
the  decussation  of  the  pyramids,  and  descend  in  the  lateral 
column  of  the  spinal  cord;  but  by  the  uncrossed  route,  they 
descend  in  the  anterior  column  of  the  cord  and  decussate, 


l86  THE   BRAIN   AND   SPINAL   CORD. 

in  succession,  through  the  white  commissure.  Impulses  by 
either  route  finally  reach  the  anterior  gray  comu  of  the 
spinal  cord  and,  with  the  exception  of  a  small  per  cent  of 
them,  they  reach  the  cornu  opposite  to  their  Eolandic  origin. 
The  few  undecussated  fibers  in  the  crossed  pyramidal  tract 
conduct  uncrossed  impulses  to  the  anterior  comu  of  the  same 
side.  Thus  are  explained  two  symptoms  of  hemiplegia,  viz., 
weakness  on  the  well  side  and  slight  motion  on  the  paralyzed 
side.  From  the  anterior  gray  cornu  of  the  spinal  cord  the 
nerve  commotions  are  conducted  by  the  efferent,  or  motor, 
fibers  of  the  spinal  nerves  to  the  muscles  of  the  neck,  trunk 
and  extremities. 

2.  Through  the  Cranial  Nerves. — Impulses  destined  to 
the  cranial  nerves  run  chiefly  from  the  lower  two-fourths  of 
the  Rolandic  area  through  corona  radiata,  genu  of  internal 
capsule  and  on,  by  the  same  path  as  the  impulses  to  spinal 
nerves,  down  to  the  point  where  they  leave  the  pyramidal 
tract  to  enter  the  nuclei  of  the  cranial  nerves,  which  they  do 
in  the  vicinity  of  the  several  nuclei.  They  enter  the  nucleus 
of  the  fourth  nerve  on  the  same  side,  but  they  cross  over  to 
the  nuclei  of  the  third,  fifth,  sixth,  seventh,  ninth,  tenth, 
eleventh  and  twelfth  cranial  nerves  of  the  opposite  side.  By 
the  above  nine  nerves  innervation  is  conducted  to  the  muscles 
of  the  orbit;  the  muscles  of  mastication,  and  expression; 
the  muscles  of  the  tongue,  palate  and  ear;  the  digastric  and 
styloid  muscles;  the  muscles  of  the  larynx,  trachea  and 
bronchi,  and  of  the  pharynx,  oesophagus,  stomach,  and  the 
intestines  down  to  the^  rectum.  And  inhibitory  impulses  are 
carried  to  the  heart. 

The  Cerebro-corticopontal  Paths,  Frontal  and  Tem- 
poral.— These  paths  are  indirect,  for  spinal  nerves,  since 
they  run  through  the  cerebellum.     Frontal. — The  impulses 


TRACING   OF    IMPULSES.  187 

originate  in  the  prefrontal  region,  at  the  anterior  end  of  the 
superior  and  at  the  foot  of  the  middle  and  of  the  inferior 
frontal  gyri,  and  descend  through  corona  radiata,  the  an- 
terior segment  of  the  internal  capsule  and  the  inner  (medial) 
fifth  of  the  crusta;  or  Temporal. — They  rise  in  the  temporal 
cortex  and  run  through  corona  radiata,  the  posterior  seg- 
ment and  inferior  lamina  of  the  internal  capsule,  and  the 
outer  (lateral)  fifth  of  the  crusta.  In  both  paths  they  run 
to  the  nucleus  pontis  of  the  same  side  and  to  motor  nuclei  of 
the  cranial  nerves,  whence  they  proceed  to  spinal  or  cranial 
nerves.  (1)  To  spinal  nerves  they  run  through  the  middle 
peduncle  of  the  cerebellum  to  the  cerebellar  cortex  and, 
thence,  continue  down  the  antero-lateral  descending  cere- 
bellar tract  to  the  anterior  gray  horn  of  the  spinal  cord. 
Their  course  from  the  cerebellar  cortex  is  through  the  resti- 
form  body,  the  lateralarea  of  the  medulla  and  the  antero- 
lateral column  of  the  cord.  From  the  gray  matter  of  the 
spinal  cord  the  impulses  are  conveyed  by  the  motor  fibers  of 
the  spinal  nerves  to  the  muscles  which  they  supply.  (2)  To 
cranial  nerves,  the  impulses  run  from  the  synapses  formed  in 
the  cranial  nuclei,  by  the  fibers  of  the  fronto-pontal  and 
temporo-pontal  tracts,  through  the  motor  fibers  of  the  nerves 
to  their  distribution. 

The  Path  Through  the  Intermediate  Bundle  of  the 
Crusta. — Cortical  impulses  of  unknown  origin  are  received 
by  the  corpus  striatum  and  conveyed  by  a  bundle  of  centrif- 
ugal axones,  which  form  the  deep  portion  of  the  crusta,  to 
the  nucleus  pontis,  chiefly  of  the  same  side.  The  impulses 
thus  traverse  the  internal  capsule  and  a  broad  but  thin  area 
in  the  crusta  just  ventral  to  the  substantia  nigra  and  dorsal 
to  the  pyramidal  tract.  From  the  nuclei  pontis,  they  proceed 
to  the  cerebellar  cortex  by  way  of  the  middle  peduncle  of  the 


188  THE    BRAIN    AND    SPINAL    CORD. 

cerebellum,  and  may  continue  down  the  descending  cerebellar 
tract  as  already  given. 

Paths  Through  the  Red  Nucleus. — There  are  two,  a 
direct  and  an  indirect.  Impulses  run  from  some  part  of  the 
cerebral  cortex  to  the  optic  thalamus  and  red  nucleus  or  to 
the  corpus  striatum  and  red  nucleus.  From  the  red  nucleus 
they  pursue  either  a  direct  or  indirect  route. 

(1)  Direct  Route. — ^By  the  direct  route,  impulses  run 
through  the  crossed  descending  tract  of  the  red  nucleus  to 
the  center  of  the  gray  crescent  in  the  opposite  side  of  the 
spinal  cord.  Crossing  the  median  raphe  at  once,  in  the  hypo- 
thalamic region,  the  impulses  descend  by  way  of  the  above 
tract  through  the  ventral  part  of  the  formatio  reticularis 
of  the  mid-brain  and  pons,  in  the  medial  part  of  the  lateral 
fillet,  then  through  the  lateral  area  of  the  medulla  among 
the  fibers  of  the  antero-lateral  ascending  cerebellar  tract,  and 
finally  down  the  spinal  cord,  through  the  dorso-lateral  portion 
of  the  crossed  pyramidal  area,  to  their  destination  in  the 
gray  matter.  From  the  center  of  the  gray  crescent  they  pro- 
ceed with  or  without  interruption  to  the  anterior  roots  of 
the  spinal  nerves,  and  are  conducted  to  the  muscles. 

(2)  Indirect  Route. — Impulses  from  the  red  nucleus  may 
also  run  through  the  superior  cerebellar  peduncle,  chiefly  the 
opposite  one,  to  the  corpus  dentatum,  and  thence,  by  axones 
from  that  nucleus,  to  the  cortex  of  the  cerebellum.  The 
descending  cerebellar  tract  continues  their  path  to  the  an- 
terior comu  of  the  cord. 

Short  Fiber  Paths. — Those  are  paths  in  the  formatio 
reticularis  chiefly.  (1)  Impulses  having  reached  the  great 
ganglia  of  the  cerebrum  and  mid-brain  may  run  down  the 
formatio  reticularis  of  mid-brain,  pons  and  medulla  and  the 


TRACING   OF   IMPULSES.  I89 

antero-lateral  ground  bundle  of  the  spinal  cord  to  the  gray 
crescent  of  the  same,  and  continue  through  the  anterior  root 
fibers  to  their  destination.  On  the  other  hand,  the  impulsefi, 
leaving  formatio  reticularis  in  mid-brain,  pons  or  medulla, 
may  enter  the  nuclei  of  motor  cranial  nerves  and  be  con- 
ducted by  them  to  tlie  muscles  supplied  by  cranial  nerves. 
(2)  The  impulses  may  leave  the  formatio  reticularis  in  the 
pons,  and  run  to  the  cerebellar  cortex  through  the  middle 
peduncle  of  the  cerebellum.  From  the  cerebellum  they  may 
follow  the  ordinary  course  through  the  descending  cerebellar 
tract  to  the  anterior  gray  horn  of  the  cord;  or  (3)  Impulses 
having  arrived  at  the  cerebellar  cortex  by  way  of  the  superior 
or  middle  peduncles,  may  descend  through  the  cerebello- 
olivary  tract,  in  the  restiform  body,  to  the  opposite  inferior 
olive,  and  be  carried  on  through  descending  axones  of  the 
olive,  in  the  antero-lateral  ground  bundle,  to  the  gray  matter 
of  the  cord  (Koelliker).  (4)  Impulses  descend  from  the 
nucleus  of  the  third  cranial  nerve  by  way  of  certain  fibers  in 
the  posterior  longitudinal  bundle  to  the  seventh  nerve,  where 
it  enters  into  the  eminentia  teres,  and  through  the  facial 
nerve  innervate  the  frontalis,  pyramidalis  nasi,  corrugator 
supercilii  and  orbicularis  palpebrarum.  Hence  these  muscles 
are  not  paralyzed  in  nuclear  facial  paralysis.  But  if  the 
lesion  be  in  the  eminentia  teres  or  distal  to  it,  then  facial 
paralysis  is  complete.  (5)  Through  certain  fibers  in  the 
posterior  longitudinal  bundle  which  rise  in  the  nucleus  of 
the  sixth  cranial  nerve  and  cross  to  the  opposite  nucleus  of  the 
motor  oculi,  impulses  run  from  the  nucleus  of  the  abducent 
through  the  opposite  third  nerve  to  the  internal  rectus  oculi. 
They  explain  the  conjugate  deviation  observed  in  lesions 
affecting  the  nucleus  of  the  sixth  nerve.  In  nudear  lesions 
of  the  abducent  nerve  the  external  rectus  of  the  same  eye 


190  THE   BRAIN   AND   SPINAL    CORD. 

and  the  internal  rectus  of  the  other  eye  are  paralyzed  if  the 
nucleus  is  destroyed  and  stimulated  if  the  nucleus  is  only 
irritated. 

II.     Afferent,  or  Sensory,  Paths. 

The  sensory  paths  conduct  two  varieties  of  impulses,  viz., 
General  and  Special..  The  impulses  originate  in  the  end- 
organs  of  the  cranial  and  spinal  nerves,  and  by  those  nerves 
are  conveyed  to  the  cerebro-spinal  axis,  through  which  they 
reach  the  proper  cortical  area  in  the  cerebrum. 

1.     General  Sensation. 

Through  Columns  of  Goll  and  Burdach. — GolFs  col- 
umn is  believed  to  carry  impul'ses  of  the  muscular  sense,  while 
impulses  of  all  varieties  of  general  sensation  are  transmitted 
by  Burdach^s  column.  Impulses  originating  in  the  end  organs 
of  the  spinal  nerves  traverse  the  dendrites  of  the  spinal 
ganglion  neurones,  the  cell-bodies  in  the  ganglia  (Cajal), 
and  then  the  axones  of  the  same.  They  enter  the  cord  through 
the  posterior  roots  of  the  spinal  nerves,  and  ascend  through 
the  tracts  of  Burdach  and  Goll,  in  the  posterior  column  of 
the  cord,  to  the  nuclei  of  that  column  in  the  medulla  oblon- 
gata, chiefly  the  nucleus  gracilis  and  nucleils  cuneatus. 
Thence  the  impulses  may  proceed  either  by  a  direct  or  by  an 
indirect  route. 

(1)  The  Direct  Route  carries  the  impulses  by  way  of  the 
interolivary  and  medial  fillet,  through  the  sensory  decussation 
of  the  medulla,  the  formatio  reticularis  of  pons  and  mid-brain 
and  the  crusta  of  the  mid-brain,  to  the  ventro-lateral  nucleus 
of  the  optic  thalamus,  from  which  they  are  conducted  by  the 
three  systems  of  Flechsig — namely,  the  anterior  stalk  of  the 
thalamus,  the  ansa  peduncularis  and  the  ansa  lenticularis — 
to  the  somsesthetic  area  of  the  cerebral  cortex.    In  their  last 


TRACING   OF   IMPULSES.  IQI 

stage  the  impulses  run  from  the  optic  thalamus  through  the 
internal  capsule  and  corona  radiata  to  the  equatorial  zone  of 
the  hemisphere. 

(2)  Indirect  Route. — By  that  route  impulses  from  the 
nucleus  gracilis  and  nucleus  cuneatus  run  to  the  cortex  of 
the  vermis  cerebelli  superior  through  the  external  arciform 
fibers;  then  on^  through  the  superior  peduncle  of  the  cere- 
bellum, to  the  red  nucleus  and  optic  thalamus.  They 
traverse  the  restiform  body  of  the  same  side,  by  way  of  the 
posterior  external  arciform  fibers;  or,  by  way  of  the  anterior 
external  arciform  fibers,  they  traverse  the  sensory  decussa- 
tion of  the  medulla  and  the  opposite  restiform  body  to  reach 
the  vermis  cerebelli  superior.  From  the  cerebellar  cortex, 
the  impulses  continue  through  cortical  axones  to  the  corpus 
dentatum,  whose  axones  conduct  them  to  the  red  nucleus  and 
optic  thalamus  of  the  opposite  side.  The  greater  number, 
therefore,  cross  over  in  the  tegmentum  of  the  mid-brain. 
Their  course  from  the  red  nucleus  and  optic  thalamus  is 
through  the  three  systems  of  Flechsig  to  the  cortex. 

Through  Cranial  Nerves  and  Medial  Fillet. — As 
crossed  fibers  from  the  terminal  nuclei  of  the  trifacial,  the 
vestibular,  the  glossopharyngeal  and  the  pneumogastric 
nerves  join  the  medial  fillet  and  run  to  the  optic  thalamus, 
so  impulses  of  common  sensation,  transmitted  by  those  cra- 
nial nerves  to  the  medulla  and  pons,  are  carried  by  the  medial 
fillet  to  the  ventro-lateral  nucleus  of  the  thalamus  on  the 
opposite  side.  The  systems  of  Flechsig,  chiefly  the  ansa 
peduncularis,  conduct  them  to  the  lower  portion  of  the 
somaesthetic  area. 

Through  Direct  Cerebellar  Tract. — Clark's  column 
of  cell-bodies  in  the  spinal  cord  receives  impulses  concerning 
equilibrium  from  the  posterior  roots  of  the  spinal  nerves  and 


192  THE    BRAIN   AND    SPINAL    CORD. 

transmits  them  at  once  to  the  direct  cerebellar  tract  through 
which  they  ascend  along  the  dorso-lateral  surface  of  the  cord, 
along  the  posterior  surface  and  through  the  restiform  body 
of  the  medulla  to  the  cortex  of  the  superior  worm  of  the 
cerebellum.  To  a  small  extent  they  cross  in  the  worm  to  the 
opposite  side.  From  the  cerebellar  cortex  the  journey  is 
completed  in  four  stages,  as  already  described,  namely: 
Corpus  dentatum,  opposite  red  nucleus,  optic  thalamus  and 
cerebral  cortex. 

Through  Antero-lateral  Ascending  Cerebellar 
Tract. — Pathetic  and  thermic  impulses  are  conveyed  by  this 
tract.  Those  impulses  enter  the  center  of  the  gray  crescent 
of  the  cord,  partly  on  the  same  side,  through  the  posterior 
nerve  roots  and  Burdach's  column.  A  large  number  decus- 
sate in  the  above  cerebellar  tract,  crossing  in  the  anterior 
commissure,  and  run  upward  through  the  antero-lateral 
ascending  cerebellar  tract  of  the  opposite  side  to  the  cortex 
of  the  superior  worm  of  the  cerebellum  and  to  the  optic 
thalamus.  In  the  cord  they  ascend  along  the  ventro-lateral 
surface.  They  run  dorsal  to  the  olive  in  the  lateral  area  of 
the  medulla  oblongata,  and  through  the  lateral  part  of  the 
formatio  reticularis  of  the  pons  to  the  angle  in  Gower's  tract. 
Prom  the  angle,  just  behind  the  quadrigeminal  bodies,  the 
greater  number  of  impulses  run  backward  with  the  tract 
through  the  valve  of  Vieussens  to  the  cortex  of  the  vermis 
cerebelli  superior;  the  remainder  run  forward  to  the  optic 
thalamus,  and  from  that  to  the  parietal  cortex.  The  common 
course  of  sensory  impulses  from  the  cerebellar  to  the  cerebral 
cortex  is,  as  already  described,  through  corpus  dentatum 
and  superior  peduncle  to  opposite  red  nucleus  and  optic 
thalamus,  though  they  may  run  through  the  middle  cere- 
bellar peduncle  to  the  pons  and  then,  by  way  of  the  formatio 


TRACING   OF   IMPULSES  I93 

reticularis,  the  medial  fillet,  or  the  posterior  longitudinal 
bundle,  ascend  to  the  optic  thalamus.  Having  arrived  in  the 
thalamus,  they  proceed  thence  by  the  three  systems  of  Flech- 
sig  to  the  soma^sthetic  cortex. 

The  Short  Fiber  Paths. — (1)  The  antero-lateral  ground 
bundle  and  formatio  reticularis  contain  ascending  axones 
which  may  convey  sensory  impulses  from  the  gray  matter  of 
the  cord,  received  from  the  posterior  roots  of  the  spinal 
nerves,  or  from  terminal  nuclei  in  medulla  and  pons  which 
receive  the  common  sensory  fibers  of  cranial  nerves,  upward 
to  the  optic  thalamus  of  the  opposite  side.  The  course  from 
the  thalamus  by  way  of  the  cortical  fillet  is  now  familiar. 

(2)  Again,  impulses  may  leave  the  formatio  reticularis  in 
the  pons  and  run  through  the  middle  cerebellar  peduncle,  by 
way  of  axones  from  the  nuclei  pontis,  to  the  cortex  of  the 
cerebellum ;  and  then  continue  by  the  ordinary  course  through 
the  superior  peduncle  to  the  red  nucleus  and  optic  thalamus. 

(3)  Certain  fibers  of  the  antero-lateral  ascending  cere- 
bellar tract  diverge  from  the  others,  in  the  medulla  oblongata, 
and  terminate  in  the  lateral  nucleus.  Impulses  of  pain  and 
temperature,  following  the  same  course,  enter  the  lateral 
nucleus,  and  are  carried  on  through  the  restiform  body  to 
the  cerebellum  by  the  tract  from  the  lateral  nucleus  to  the 
cerebellar  cortex,  thence  to  the  somsesthetic  area  as  previously 
given. 

Destruction  of  any  of  the  above  sensory  paths  causes  loss 
of  the  especial  variety  of  impulse  which  travels  that  path. 
Destruction  of  G  oil's  column  produces  loss  of  muscular  sen- 
sations, and  cases  are  on  record  in  which  a  cord  lesion 
abolished  pain  and  temperature  seusations  while  touch  was 
not  affected. 


194  the  brain  and  spinal  cord. 

2.     Special  Sensations. 

Impulses  producing  the  sensations  of  smell,  sight,  hearing 
and  taste  are  carried  from  the  respective  organs  of  sense  to 
the  brain  by  the  following  nerves:  The  Olfactory;  the 
Optic;  the  Auditory;  and  the  Glossopharyngeal,  chorda 
tympani  and  pars  intermedia. 

Olfactory  Path. — Impulses  of  smell  originate  in  the 
upper  third  of  the  Schneiderian  membrane.  They  run 
through  the  olfactory  nerves  to  the  second  layer  in  the  bulb, 
where  they  are  transferred  to  the  dendrites  of  the  mitral 
cells.  By  the  axones  of  the  mitral  cells  they  are  carried 
backward  through  the  olfactory  tract  and  roots  to  the  cere- 
bral hemisphere.  The  internal,  or  medial,  root  conducts 
them  to  the  area  of  Broca  and  anterior  end  of  the  gyrus  f orni- 
catus,  whence  through  the  cingulum  and  uncinate  fasciculus 
they  reach  the  cortical  area  of  smell  in  the  uncus  hippocampi. 
By  the  middle  olfactory  root  the  impulses  enter  the  trigone 
and  complete  their  journey  either  in  the  same  manner  as 
given  above  or  via  the  anterior  commissure.  The  external, 
or  lateral,  root  of  the  olfactory  tract  conducts  the  impulses 
directly  to  the  uncus  of  the  hippocampal  convolution.  Note 
that  olfactory  impulses  are  chiefly,  if  not  entirely,  uncrossed. 

Optic  Path. — ^Impulses  of  sight  originate  in  the  rods  and 
cones  of  the  retinae  and  traverse  three  or  more  series  of 
neurones  to  the  terminal  nuclei  of  the  optic  tracts;  namely, 
the  rod  and  cone,  the  bipolar  and  the  ganglionar  neurones. 
The  axones  of  the  last  form  the  optic  nerves  arid  the  visual 
part  o-f  the  optic  tracts.  From  the  right  halves  of  both 
retinae  and  from  the  left  halves  of  both,  impulses  run  through 
the  corresponding  tract  to  the  external  geniculate  body  and 
the  pulvinar  of  the  optic  thalamus;  also  to  the  superior 
quadrigeminal  body  and  the  nudeus  of  the  motor  oculi  nerve. 


TRACING    OF    IMPULSES.  I95 

The  two  latter  produce  ocular  and  pupillary  reflexes.  From 
the  lateral  geniculate  body  and  pulvinar  the  optic  radiations 
carry  the  impulses  through  the  posterior  segment  of  the  in- 
ternal capsule  to  the  half-visual  center  in  the  cuneus  and 
(to  a  small  extent)  the  convex  part  of  the  occipital  lobe. 
Impulses  from  the  nasal  halves  of  the  retinae  decussate  in  the 
optic  commissure;  those  from  the  temporal  halves,  for  the 
most  part  at  least,  remain  on  the  same  side,  but  a  few  may 
cross  through  the  quadrigeminal  bodies  and  superior  brachia. 
Auditory  Paths. — There  are  two  auditory  paths,  the 
Cochlear  and  the  Vestibular.  The  former  is  concerned  with 
hearing  and  the  latter  with  equilibrium. 

1.  The  Cochlear  Path. — Impulses  of  hearing  originate 
in  the  organ  of  Corti.  They  are  transmitted  by  the  rods 
and  hair  cells  of  Corti  to  the  dendrites  of  the  spiral  ganglion. 
Traversing  the  dendrites  and  cell-bodies  of  that  ganglion,  they 
enter  the  axones,  which  form  the  cochlear  nerve,  and  run 
backward  to  the  terminal  nucleus  of  that  nerve  in  the  me- 
dulla. Both  the  ventral  and  the  dorsal,  or  lateral,  portions 
of  the  cochlear  nucleus  (ventral  auditory  nucleus)  receive 
the  impulses  of  hearing.  From  the  cochlear  nucleus  they 
run  either  lateral  and  dorsal  to  the  restiform  body  and  cross 
to  the  opposite  side  through  the  acustic  striae  and  trapezium, 
or  they  run  medial  to  the  restiform  body  and  enter  at  once 
into  the  trapezium.  By  either  course  they  reach  the  lateral 
fillet,  and  chiefly  the  opposite  one.  The  lateral  fillets  con- 
duct the  impulses  to  the  inferior  quadrigeminal  bodies;  the 
inferior  brachia  to  the  internal  geniculate  bodies,  and  the 
acustic  radiations  to  the  third  and  fourth  fifths  of  the  supe- 
rior temporal  and  to  the  transverse  temporal  gyri  of  the 
cerebrum. 

2.  Vestibular  Path. — The  extent  of  the  vestibular  conduc- 


196  THE    BRAIN   AND    SPINAL    CORD. 

tion  path  is  from  the  acustic  areas  of  the  utricle  saccule  and 
semi-circular  canals  to  the  vestibular  nuclei  in  the  floor  of  the 
fourth  ventricle  and,  thence,  to  the  cerebellum  and  the  corti- 
cal area  of  equilibrium  in  the  parietal  cortex.  It  is  the  path 
of  the  space  sense.  Through  the  vestibular  nerve  the  im- 
pulses reach  the  dorso-medial,  dorso-lateral  and  superior 
auditory  (vestibular)  nuclei  in  the  floor  of  the  fourth  ven- 
tricle and  the  spinal  nucleus,  which  has  not  been  definitely 
located,  and  they  probably  reach  the  nuclei  in  the  cerebellum 
also  (globosus  and  fastigii).  The  impulses  may  pursue, 
from  the  terminal  nuclei  in  the  ventricular  floor,  either  a 
direct  or  an  indirect  course  to  the  cerebral  cortex. 

(1)  By  the  direct  course  they  run  through  the  opposite 
medial  fillet  and  certain  fibers  in  the  three  systems  of  Flech- 
sig(?). 

(2)  The  impulses  run  to  the  cerebellum,  by  the  indirect 
course,  through  the  acustico-cerebellar  tract,  and  probably 
through  uninterrupted  fibers  of  the  vestibular  nerve  in  the 
restiform  body.  They  thus  reach  the  opposite  nucleus 
fastigii  and  nucleus  globosus;  perhaps  a  number  also  reach 
the  corpus  dentatum  and  cerebellar  cortex.  From  the  cere- 
bellum the  course  of  the  impulses  is,  presumably,  through 
the  superior  peduncle  to  the  red  nucleus  and  optic  thalamus 
of  both  sides  and  thence  to  the  cortex.  They  may  excite  in 
the  cerebellum  impulses  of  equilibration  which  descend  to 
the  motor  nuclei  of  spinal  nerves  in  the  anterior  horns  of  gray 
matter  by  way  of  the  antero-lateral  descending  cerebellar 
tracts. 

Impulses,  believed  to  be  concerned  with  reflexes,  run  from 
the  vestibular  nuclei  in  the  floor  of  the  fourth  ventricle  (a) 
to  opposite  nuclei  of  motor  cranial  nerves  via  the  posterior 
longitudinal  bundle;  (b)  to  the  quadrigeminal  bodies  through 


TRACING   OF    IMPULSES.  197 

the  superior  and  lateral  fillets;  and  (c)  to  the  inferior  olive 
and  lateral  column  of  the  spinal  cord  by  way  of  the  vestibnlo- 
olivary  and  vestibulo-spinal  fibers. 

The  Gustatory  Paths. — They  extend  from  the  tongue  to 
the  glossopharyngeal  nucleus  in  the  medulla  and  thence 
through  the  opposite  medial  fillet  and  inferior  lamina  of  the 
internal  capsule  to  the  taste  area  in  the  gyrus  hippocampi. 
There  are  two  paths  from  the  tongue  to  the  ninth  nucleus. 
Those  impulses  from  the  base  of  the  tongue  and  the  palate 
run  through  the  ninth  nerve  and  those  from  the  anterior 
two-thirds  of  the  tongue  through  the  chorda  tympani  and  pars 
intermedia  to  the  medulla  (A.  F.  Dixon)  (see  note).  Pos- 
sibly, gustatory  impulses  originating  in  the  palate  may 
traverse  the  descending  branches  of  Meckel's  ganglion  and 
the  great  superficial  petrosal  nerve  to  reach  the  geniculate 
ganglion  on  the  facial ;  and,  then,  continue  through  the  pars 
intermedia  to  the  glossopharyngeal  nucleus.  All  impulses 
arriving  at  this  nucleus  complete  their  journey  in  two  stages: 
First,  through  the  medial  fillet  to  the  opposite  thalamus; 
and,  second,  through  internal  capsule  to  the  hippocampal 
cortex. 

Destruction  of  the  olfactory  conduction  path  on  one  side 
causes  anosmia  on  the  same  side ;  of  the  optic  tract  or  radia- 
tions, hemianopia  in  the  corresponding  halves  of  both  retinae ; 
of  the  auditory  path  above  the  pons,  deafness  chiefly  on  the 
opposite  side;  and  interruption  of  the  gustatory  path  above 
the  medulla  oblongata  abolishes  taste  on  the  opposite  (?) 
side. 


Note.— Edinbg.  M.  J.,  1897,  Vol.  I,  p.  395,  A.  F.  Dixon. 

Amer.  J.  Med.   Science,  1898,   Vol.   I,   pp.  502-532,   Cases  VI  and 
VII,  Keen  and  Spiller. 


198  THE    BRAIN    AND    SPINAL    CORD. 

III.     Keflex  Paths. 

There  is  no  visible  limit  to  the  number  of  reflex  paths. 
Hence  no  attempt  will  be  made  to  give  them  completely,  but 
a  few  examples  of  various  kinds  will  be  given  which  may 
assist  the  student  to  trace  others  and  be  suggestive  of  their 
great  multiplicity  and  importance. 

Eeflex  arcs  are  formed  ( 1 )  by  the  sensory  and  motor  fibers 
of  spinal  nerves,  associated  in  the  gray  matter  of  the  cord; 
(2)  by  the  sensory  and  motor  fibers  of  cranial  nerves,  which 
are  connected  in  the  brain;  (3)  by  afferent  spinal  fibers,  the 
posterior  longitudinal  bundle,  chiefly,  and  efferent  cranial 
fibers;  and  (4)  by  afferent  cranial  and  efferent  spinal  nerve 
fibers,  the  two  being  associated  by  the  anterior  longitudinal 
bundle,  the  spinal  root  of  the  fifth  nerve,  the  vestibulo- 
olivary  and  vestibulo-spinal  tracts,  the  solitary  bundle,  etc. 

(1)  Spinal  Reflexes. — In  the  simplest  spinal  reflexes^ 
the  afferent  fibers  of  the  arc  arborize  about  the  cell-bodies 
whose  axones  constitute  the  efferent  fibers.  Among  them  are 
the  skin  and  muscle  reflexes,  such  as  the  plantar,  the  patellar, 
the  gluteal  and  the  cremaster  reflexes,  the  involuntary  with- 
drawing of  a  part  from  a  source  of  irritation,  etc. 

More  complicated  spinal  reflexes  are  those  of  defecation, 
micturition,  parturition,  vasomotor  reflexes,  cardio-accelera- 
tor  reflexes,  etc.  The  impulses  traverse  at  least  three  neurones 
in  these  reflexes.     As  an  example,  trace  a  defecation  reflex. 

Defecation  Befiex. — ^The  rectum  is  supplied  by  the  third 
and  fourth  sacral  nerves  and  by  branches  of  the  inferior 
mesenteric  and  hypogastric  plexuses.  Irritation  of  the  sen- 
sory endings  in  the  mucous  membrane  is  caused,  normally,  by 
the  presence  of  feces.  The  impulses  caused  thereby  run  to 
the  special  defecation  center  in  the  lumbar  enlargement  of  the 
spinal  cord,  either  by  way  of  the  sacral  nerves  or  through 


TRACING  OF    IMPULSES.  199 

the  sympathetic  plexuses,  the  ganglionated  cord,  and  the 
rami  communicantes  to  the  lumbar  nerves,  through  the  pos- 
terior roots  of  which  they  reach  the  center  in  the  cord.  From 
the  defecation  center  the  impulses  pursue  two  courses:  (a) 
They  descend  through  the  third  and  fourth  sacral  nerves 
and  cause  inhibition  in  the  circular  fibers  of  the  rectum  and 
contraction  of  the  longitudinal  muscle,  (b)  This  action  is 
immediately  followed  by  impulses  which  pursue  the  sympa- 
thetic course,  through  the  anterior  roots  of  the  lumbar  nerves, 
the  rami  communicantcs,  the  ganglionated  cord,  and  the  in- 
ferior mesenteric  and  hypogastric  plexuses,  to  the  rectum. 
They  cause,  in  succession  from  above  downward,  contraction 
of  the  circular  muscle  of  the  rectum.  The  two  series  of 
impulses  thus  open  a  way  for  the  passage  of  fecal  matter; 
and,  then,  force  it  through  the  opening  unless  prevented  by 
the  voluntary  contraction  of  the  external  sphincter. 

(2)  Cranial  Reflexes. — The  simplest  of  these  reflexes 
are  such  as  spasm  of  the  muscles  of  mastication  caused  by  a 
bad  tooth,  in  which  both  limbs  of  the  arc  are  formed  by  the 
trifacial  nerve.  Again,  the  facial  expression  of  pain  due  to 
the  same  cause.  In  this  the  impulses  traverse  the  trifacial 
nerve  and  by  the  collaterals  of  its  root-fibers  reach  the  nucleus 
of  the  facial.  Through  the  facial  they  cause  contraction  of 
certain  muscles  of  expression. 

Salivary  reflexes,  in  which  the  sight  of  a  fine  dinner  or 
the  smell  of  it  causes  the  flow  of  saliva;  coughing,  sneezing, 
vomiting  reflexes  and  deglutition  reflexes  are  more  compli- 
cated, but,  knowing  the  nerve  supply  of  the  parts  involved, 
the  student  can  trace  the  impulses. 

(3)  Spinal  and  Cranial  Reflexes. — Impulses  received 
by  the  spinal  cord  through  the  afferent  fibers  of  its  nerves 
are  transmitted  by  the  posterior  longitudinal  bundle  to  the 


200  THE    BRAIN   AND    SPINAL    CORD. 

nuclei  of  motor  cranial  nerves,  or,  perhaps,  through  Burdach's 
column  and  the  interolivary  fillet  to  the  same  nuclei.  Thus 
is  brought  about  the  movement  of  the  eyes  toward  the  source 
of  impulse,  a  change  of  facial  expression  to  agree  with  the 
painful  or  pleasing  character  of  the  impulses,  etc. 

(4)  Cranial  and  Spinal  Reflexes. — Of  these  there  are 
many.    Let  us  notice  three. 

Respiratory  Reflex. — Any  obstruction  or  irritation  in  the 
larynx  or  trachea  sends  an  impulse  through  the  pneumo- 
gastric  nerve  to  its  sensory  nucleus  and,  through  its  descend- 
ing branches,  in  the  solitary  bundle,  to  the  nucleus  ambiguus 
and  nucleus  of  the  phrenic  nerve  in  the  cervical  cord,  causing 
increased  respiratory  effort,  coughing,  spasm  of  muscles 
closing  the  glottis,  etc. 

Auditory  Reflex. — Turning  of  the  head  upon  hearing  a 
sound,  and  the  sudden  starting,  caused  by  hearing  a  loud 
sound,  are  illustrations  of  this  reflex.  The  path  for  the 
latter  is  probably  as  follows:  The  auditory  nerve,  the  vesti- 
bulo-olivary  and  vestibulo^spinal  tracts,  antero-lateral  ground 
bundle  and  efferent  fibers  of  spinal  nerves. 

Pupillary  Reflexes. — Pupillary  reflexes  belong  to  the  cra- 
nial and  cranio-spinal  group  of  reflexes.  The  cilio-spinal 
centers  are  in  the  cervical  enlargement  of  the  spinal  cord, 
the  pupillo-dilator  in  the  upper  and  the  pupillo-constrictor  in 
the  middle  part  of  that  enlargement.  They  receive  optic  im- 
pulses through  the  anterior  (or  ventral)  longitudinal  bundle 
from  the  corpora  quadrigemina  superiora.  The  superior 
quadrigeminal  bodies  receive  those  impulses  by  two  routes: 
First,  directly,  through  the  fibers  of  the  external  root  of  the 
optic  tract,  and,  second,  indirectly,  through  centrifugal  fibers 
in  the  optic  radiations,  and  the  superior  brachium.  By  the 
latter  route,  the  optic  impulses  which  have  xeached  the  visual 


TRACING   OF   IMPULSES.  201 

area  of  the  occipital  lobe,  by  way  of  the  intrinsic  retinal 
neurones  and  the  optic  nerves,  tracts  and  radiations,  are 
returned  to  the  optic  thalamus  and  external  geniculate  body 
and  then  carried  back  to  the  superior  quadrigeminal  bodies. 
Thence,  reaching  the  cilio-spinal  centers  through  the  anterior 
longitudinal  bundle,  the  impulses  take  one  of  two  courses: 
(a)  They  leave  the  spinal  cord  through  the  anterior  roots  of 
the  upper  thoracic  nerves  and  run,  in  succession,  through  the 
rami  communicantes,  the  cervical  cord  of  the  sympathetic, 
the  cavernous  plexus^  the  ciliary  ganglion  and  the  short 
ciliary  nerves  to  the  radiating  fibers  of  the  iris,  causing  dila- 
tion of  the  pupil,  (b)  From  the  pupillo-constrictor  center, 
the  impulses  are  carried  upward  by  the  posterior  longitudinal 
bundle  to  the  nuclei  of  the  motor  oculi  nerve,  where  they  are 
reinforced  by  optic  impulses  received  directly  through  the 
superior  quadrigeminal  body  and  posterior  commissure.  The 
impulses  reach  the  ciliary  muscle  and  the  circular  muscle  of 
the  iris  through  the  motor  oculi,  ciliary  ganglion  and  short 
ciliary  nerves.  The  results  are  contraction  of  the  pupil  and 
accommodation  for  distance. 


CHAPTER  XI. 


EMBRYOLOGY  OF  THE  BRAIN  AND  SPINAL  CORD. 

The  brain  and  spinal  cord  are  developed  from  the  neural 
tube;  the  spinal  and  sympathetic  ganglia  and  the  ganglia  of 
sensory  cranial  nerves  are  derivatives  of  the  neural  crest. 

Very  soon  after  conception  there  appears  along  the  median 
line,  in  the  back  of  the  embryo,  a  plate  of  epiblast,  called  the 
medullary  plate.  That  plate  soon  presents  two  longitudinal 
elevations,  the  medullary  ridges,  separated  by  a  median  fur- 
row, the  neural  groove.  The  rapid  growth  and  infolding  of 
the  medullary  ridges  roofs  over  and  closes  in  the  neural 
groove  and  thus  forms  the  neural  tube.  That  approxima- 
tion of  the  medullary  ridges  produces  a  slight  median  eleva- 
tion, which  is  the  neural  crest.  By  the  fifteenth  day  after 
conception  the  neural  tube  and  crest  are  complete,  except 
posteriorly,  where  the  neural  groove  is  stiU  open. 

Meninges. — Later  the  neural  tube  becomes  surrounded  by 
mesoblast  which  forms  the  pia  mater,  arachnoid  and  dura 
mater. 

The  Neural  Crest. — (1)  The  cephalic  portion  of  the  neural 
crest  becomes  broken  into  five  pairs  of  ganglia,  which,  during 
development,  shift  their  positions  to  the  ventral  side  of  the 
brain.  Those  ganglia  are  called  the  Jugular,  Petrosal,  Genic- 
ulate, Auditory  and  Gasserian.  They  give  origin  to  the 
sensory  parts  of  the  pneumogastric,  glossopharyngeal  and 
facial  nerves;  all  of  the  auditory  nerve,  and  the  sensory  part 
of  the  trifacial.     In  all  of  the  ganglia,  except  the  auditory, 


EMBRYOLOGY   OF  THE    BRAIN   AND    SPINAL    CORD.       2O3 

the  cells  develop  into  unipolar  neurones ;  they  remain  bipolar 
in  the  auditory  ganglion.  The  single  processes  of  the  uni- 
polar neurones  immediately  divide,  T-like,  into  peripheral 
and  central  fibers,  which  in  appearance  are  axones.  The 
peripheral  fibers  form  the  sensory  part  of  the  respective 
nerves  and  conduct  impulses  toward  the  cell-body,  hence  they 
may  be  considered  dendrites  (Cajal) ;  the  central  fibers,  the 
axones  proper,  form  the  part  of  the  sensory  nerve  between 
the  ganglion  and  the  brain.  From  the  auditory  ganglion, 
which  moves  backward  to  a  point  behind  the  geniculate 
ganglion,  the  dendrites  run  outward  to  the  acustic  areas  of 
the  internal  ear;  the  axones  enter  the  medulla  oblongata. 
All  the  central  axones  of  the  several  ganglia  divide,  T-like, 
upon  entering  the  brain,  and  collaterals  rise  from  the  un- 
divided fibers  and  from  both  branches  of  them.  These 
axones  and  collaterals  arborize,  chiefly,  in  the  terminal  nuclei 
of  the  respective  nerves;  but  certain  of  them,  the  excito- 
reflex  fibers,  terminate  in  nuclei  of  motor  nerves. 

(2)  The  spinal  portion  of  the  neural  crest  forms  the 
thirty-one  pairs  of  Spinal  Ganglia  situated  on  the  posterior 
nerve-roots ;  and,  also,  the  Vertebral,  Prevertebral  and  Termi- 
nal  Ganglia  of  the  sympathetic  system.  The  sympathetic 
ganglia  wander  widely.  In  them  the  epiblastic  cells  develop 
into  multipolar  neurones,  the  nonmedullated  processes  of 
which  constitute  the  larger  number  of  gray  fibers  in  the 
sympathetic  system.  The  cells  of  the  spinal  ganglia  form 
unipolar  neurones,  like  those  of  the  jugular,  petrosal,  genicu- 
late and  Gasserian  ganglia.  Like  them,  also,  the  single 
processes  divide,  T-like,  the  peripheral  arms  of  the  T- 
branches  forming  the  sensory  part  of  each  spinal  nerve  and 
the  central  arms  (the  axones)  the  posterior  roots  of  those 
nerves.     The  latter  enter  the  cord  at  the  postero-lateral  fis- 


204  THE    BRAIN    AND    SPINAL    CORD. 

sure  and,  before  and  after  dividing  T-like  into  an  ascending 
and  a  descending  branch,  give  off  collaterals.  The  descending 
fibers  (axones  and  collaterals)  arborize  in  the  gray  matter  of 
the  cord;  the  ascending  axones  and  collaterals  terminate 
chiefly  in  the  spinal  cord,  and  in  the  nuclei  of  its  posterior 
columns,  namely,  the  nucleus  gracilis  and  nucleus  cuneatus. 
A  few  ascending  fibers  end  in  the  cerebellum  and  cerebrum. 

The  Neural  Tube.— It  is  well  formed  at  the  fifteenth  day. 
The  cephalic,  or  closed,  end  of  the  tube  is  much  larger  than 
the  caudal  end,  and  presents  at  this  time  two  constrictions 
that  separate  the  Primary  Brain  Vesicles  from  one  another — 
the  anterior,  the  middle  and  the  posterior.  Behind  the  poste- 
rior primary  vesicle,  the  neural  tube  remains  small  and  of 
nearly  uniform  size ;   that  part  forms  the  spinal  cord. 

The  neural  tube,  up  to  the  fourth  week,  is  composed  of  a 
single  layer  of  long  columnar  cells  whose  ends  form  the  exte- 
rior and  interior  surfaces  of  the  tube.  The  cells  contain  a 
nucleus  in  their  middle  third  and  present  a  central  and  a 
peripheral  clear  zone.  In  the  central  clear  zone,  near  the 
interior  surface  of  the  tube,  there  may  be  observed  between 
the  fourth  and  the  fifth  week  a  number  of  small,  round, 
nucleated  cells,  the  nuclei  of  which  are  in  all  stages  of 
karyokinesis.  These  are  the  germinating  cells  (His) .  Soon 
they  become  elongated  and  send  out  a  protoplasmic  process 
from  what  was  originally  (i.  e.,  before  the  formation  of  the 
neural  tube)  the  deep,  or  proximal,  end  of  the  cell.  Now 
they  are  neuroblasts,  because  they  are  the  parents  of  the 
neurones.  The  protoplasmic  processes  form  the  axones,  and 
other  processes  may  or  may  not  develop.  Both  the  axones 
and  dendrites  grow  in  the  direction  of  least  resistance  (His). 
While  the  neuroblasts  are  developing,  the  columnar  cells  of 
the  neural  tube  undergo  great  changes.     They  become  more 


EMBRYOLOGY   OF   THE    BRAIN    AND    SPINAL    CORD.       205 

and  more  elongated  and,  by  a  process  of  vacuolation,  their 
protoplasm  becomes  perforated  and  branched  and  so  broken 
up  a;S  to  entirely  destroy  the  original  outlines  of  the  cells. 
The  branches  appear  to  unite  and  form  a  sort  of  radial 
net-work  in  the  peripheral  clear  zone,  called  the  myelospon- 
yium.  The  elements  of  the  myelospongium  are  the  spongio- 
blasts; they  form  the  neuroglia.  At  this  time  the  Three 
Histologic  Layers  begin  to  show,  namely,  (1)  the  outer  layer 
(neuroglia),  (2)  the  middle,  or  mantle,  layer,  composed  of 
neuroblasts,  and  (3)  the  inner,  or  ependymal,  layer;  also  at 
this  time  a  lateral  longitudinal  groove  appears,  which  extends 
from  the  mesencephalon  to  the  caudal  end  of  the  tube.  The 
groove  is  on  the  ventricular  surface.  It  gives  the  lumen  of 
the  tube  a  diamond  shape,  on  section,  and  separates  the 
ventral  from  the  dorsal  zone.  The  ventral  zone  is  motor  and 
the  dorsal  is  sensory. 

BRAIN. 

The  brain  vesicles  grow  rapidly.  By  the  end  of  the  fourth 
week  a  constriction  is  visible  in  the  anterior  primary  vesicle 
and  another  in  the  posterior  primary  vesicle,  dividing  each 
into  two  and  making  in  all  Five  Secondary  Brain  Vesicles, 
which  freely  communicate  with  one  another  and  are  numbered 
from  before  backward.     They  are: 

1.  Prosencephalon,  or  telencephalon. 

2.  Thalamencephalon,  or  diencephalon. 

3.  Mesencephalon. 

4.  Epencephalon. 

.  5.  Metencephalon,  or  myelencephalon. 

These  vesicles  form  the  brain,  their  cavities  becoming  the 

ventricles.     The  neuroblasts   of   the  mantle  layer   produce 

the  neurones,  whose  cell-bodies  and  dendrites  are  found  in 

the  cortex  and  ganglia,  and  whose  medullated  axones  form 


206  THE    BRAIN   AND   SPINAL    CORD. 

the  white  substance.    The  supporting  neuroglia  is  formed  by 
the  spongioblasts  of  the  neurogliar  and  ependymal  layers. 

Flexures. — The  cephalic  portion  of  the  neural  tube  is  the 
seat  of  three  flexures,  two  ventral  and  one  dorsal.  (1)  The 
mesencephalic  flexure  (ventral)  begins  very  early  and 
amounts  to  nearly  180  degrees  by  the  twenty-eighth  day.  It 
bends  ventrally  the  thalamencephalon  until  it  almost  touches 
the  epencephalon.  Thus  the  inter-brain  and  pons  are  ap- 
proximated. (2)  The  cervical  flexure  is  also  a  ventral  one, 
It  is  located  at  the  junction  of  the  fifth  vesicle  with  the  spinal 
cord,  and  corresponds  to  the  bending  of  the  head  upon  the 
body  of  the  embryo.  This  flexion  begins  about  the  twenty- 
first  day.  By  the  end  of  the  fourth  week,  it  is  completed 
and  amounts  to  90  degrees.  (3)  The  dorsal  flexure  is  be- 
ginning to  form  at  the  same  time  (fourth  week).  It  occurs 
between  the  fourth  and  fifth  brain  vesicles,  and  is  often 
called  the  metencephalic  flexure.  It  reaches  180  degrees  by 
the  eighth  week,  when  the  dorsal  part  of  the  epencephalon 
(the  cerebellum)  rests  upon  the  metencephalon  (the  medulla 
oblongata).  The  cervical  and  metencephalic  flexures  almost 
entirely  disappear,  but  the  mesencephalic  flexure  is  perma- 
nent.    . 


EMBRYOLOGY   OF   THE    BRAIN   AND    SPINAL   CORD. 


207 


TABLE    III. 


BEAIN    VESICLES     AND    THEIB    DEBIVATIVES. 


Primary  Vesicles. 


Secondary  Vesicles. 


'  1st.    The  Prosenceph-  *j 
alon. 


Anterior 

(Fore-brain) 


2d. 


The    Thalamen- 
cephalon. 


Middle 

(Mid-brain). 


3d.    The  Mesencepha- 
lon. 


Derivatives  and 
Ventricles. 
Hemispheres  and  An- 
terior wall  of  third 
ventricle.  (Foram- 
ina of  Monro, 
lateral  ventricles, 
hemispheres,  cor- 
pora striata,  olfac 
tory  lobes,  fornix, 
anterior  commis- 
sure, corpus  cal- 
losum  and  lamina 
terminalis.) 

Inter-brain  and 
third  ventricle,  ex- 
cept anterior  wall. 
(Optic  thalami,  ex- 
ternal geniculate 
bodies,  posterior 
and  middle  com- 
missures, pineal 
body,  roof  epithe- 
lium of  third  ven- 
tricle and  the  third 
ventricle,  corpora 
albicantia,  tuber 
cinereum  and  in- 
fundibulum,  lami- 
na cinerea,  retinae, 
optic  nerves, 
chiasm  and 
tracts.) 

Mid-brain  and  Aqe- 
duct  of  Sylvius. 
(Crustae,  substan- 
tia nigra,  tegmen- 
tum. Sylvian  aque- 
duct, corpora  qua*- 
rigemina  and  in- 
ternal geniculate 
bodies.) 


208  THE    BRAIN    AND    SPINAL    CORD. 


Posterior 

(Hind-brain).  J 


4th.  TheEpencepha.  rHi"4~^  JJ^^ e  g 

""'■                   I      lum.)  •      <! 

5th.  TheMetencepha- r  After^^^^^^^^^  | 

^°^-                   I      ta.)  P 


The  cerebrum  is  developed  from  the  anterior  primary 
brain  vesicle  as  is  shown  in  the  outline;,  being  the  more  im- 
mediate descendant  of  the  prosencephalon  and  thalamen- 
cephalon. 

PROSENCEPHALON. 

It  is  at  first  a  single  vesicle  forming  the  fore  part  of  the 
anterior  primary  vesicle.  The  median  portion  of  its  ante- 
rior wall  (lamina  terminalis)  remains  almost  stationary; 
laterally,  it  is  the  seat  of  rapid  growth  and  produces  on  either 
side  a  hollow  diverticulum,  whose  cavity  is  the  primitive 
lateral  ventricle  and  whose  walls  form  the  substance  of  the 
hemisphere.  The  outgrowth  is  called  th^  hemisphere  vesicle, 
its  constricted  stalk  contains  the  primitive  foramen  of  Monro. 
The  vesicles  grow  forward  and  outward  at  first,  separated 
from  one  another  by  mesoblast  which  forms  the  falx.  Later, 
growth  occurs  in  succession,  upward,  backward  and  down- 
ward, until  by  the  seventh  month  the  hemisphere  overhangs 
every  other  part  of  the  brain. 

Olfactory  Lobe. — In  the  fifth  week  a  hollow  diverticulum 
grows  out  from  the  antero-inferior  wall  of  the  hemisphere 
vesicle  and  forms  a  prominent  lobe.  It  preserves  a  lobular 
form  in  the  horse,  and  in  some  other  animals;  but  in  man 
it  soon  becomes  constricted  by  the  fissura  prima  into  an 
anterior  and  a  posterior  lobule,  and  loses  its  ventricular  cav- 
ity. The  anterior  olfactory  lobule  develops  the  olfactory 
bulb,  tract,  trigone,  and  the  area  of  Broca;  the  posterior 
lobule  forms  the  anterior  perforated  lamina. 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.        2O9 

Primary  Sulci. — The  vesicle  walls  are  of  uniform  thinness 
up  to  the  second  month,  being  composed  of  a  single  layer  of 
columnar  cells.  During  their  rapid  gro^\i;h  in  the  second 
and  third  months  they  become  thrown  into  folds  which  en- 
croach upon  the  cavity  and  present  on  the  surface  of  the 
vesicle  (or  hemisphere)  the  primary  sulci.  The  cause  of  the 
infoldings  is,  perhaps,  the  resistance  of  the  slower  growing 
cranium.  The  primary  sulci  are  best  developed  in  the  third 
month.  Their  location  nearly  corresponds  to  the  following 
permanent  fissures:  Sylvian,  Parieto-occipital,  Calcarine, 
Hippocampal,  Collateral  and  Anterior  Great  Transverse 
(choroid)  fissure.  The  hippocampal  fissure  is  the  inferior 
part  of  the  Fissura  Prima.  The  superior  part  of  the  latter 
corresponds  to  the  fissure  of  the  corpus  callosum,  and  the 
anterior,  which  is  transverse,  separates  the  olfactory  trigone 
from  the  anterior  perforated  space.  For  the  most  part  the 
primary  sulci  have  disappeared  by  the  first  of  the  fifth  month 
(at  this  stage  the  cranium  grows  more  rapidly  than  the  brain 
vesicles)  ;  but  the  ventricular  eminences  produced  by  the 
sulci  are  permanent,  namely,  the  hippocampus  major  and 
minor  and  eminentia  coUateralis.  Possibly  the  caudate 
nucleus  belongs  in  the  same  group. 

Permanent  Fissures. — In  the  sixth  month  the  primary 
sulci  are  replaced  by  the  important  permanent  fissures,  which 
divide  the  hemisphere  into  lobes.  Many  of  the  smaller  jier- 
manent  sulci  appear  after  birth.  The  permanent  fissures,  or 
sulci,  are  the  result  of  depressions  in  the  surface;  they  do 
not  involve  the  whole  thickness  of  the  ventricular  wall.  Their 
object  is  probably  to  preserve  a  certain  ratio  between  the 
cortex  and  the  white  matter  in  the  hemisphere.  (For  the 
permanent  fissures,  see  Exterior  Surface  of  the  Cerebrum.) 
Two  of  the  permanent  fissures  are  peculiar,  namely : 


210  THE    BRAIN   AND   SPINAL    CORD. 

(1)  The  Fissure  of  Sylvius  is  formed  by  the  approxima- 
tion of  the  anterior  and  posterior  walls  of  the  broad  Sylvian 
valley,  or  primary  sulcus,  in  the  ventral  border  of  the  hemi- 
sphere. The  bottom  of  the  valley  develops  the  corpus 
striatum  and  the  island  of  Eeil.  The  latter  is  concealed  be- 
fore birth  by  a  backward  and  downward  growth  of  the  an- 
terior wall,  forming  the  orbital,  frontal  and  fronto-parietal 
opercula.  The  forward  and  downward  growth  of  the  poste- 
rior wall  completes  the  fissure  and  forms  the  temporal  lobe. 

(2)  The  Anterior  Great  Transverse  Fisswe,  or  Choroid 
Fissure. — It  is  produced  by  a  curved  invagination  of  the 
medial  wall  of  the  hemisphere  vesicle.  Beginning  just  be- 
hind the  stalk  of  the  vesicle,  which  contains  the  foramen  of 
Monro,  it  extends  backward  to  a  point  opposite  to  the  poste- 
rior end  of  the  optic  thalamus,  and  then  bends  downward 
and  forward  toward  the  apex  of  the  temporal  lobe.  It  in- 
volves the  entire  thickness  of  the  vesicle  wall,  though  it  is  a 
permanent  fissure,  and  the  fold  which  it  pushes  into  the 
lateral  ventricle  persists  as  a  single  layer  of  epithelium  in- 
vesting the  choroid  plexus,  hence  the  name  fissura  choroidea. 
In  the  developed  brain  the  anterior  great  transverse  (cho- 
roid) fissure  is  situated  between  the  fornix  and  the  taenia 
semicircularis. 

Thickenings. — The  walls  of  the  hemisphere  vesicle  thicken 
rapidly  as  the  vesicle  grows  in  size,  and  form  the  cortical  and 
medullary  substance.  By  the  end  of  the  second  month  the 
corpus  striatum  is  well  formed,  near  the  middle  of  the  floor 
of  the  hemisphere;  and  a  ridge  appears  about  the  same  time 
in  the  medial  wall  of  the  vesicle  along  the  convexity  of  the 
anterior  great  transverse  fissure.  That  ridge  develops  into 
a  bundle  of  fibers  constituting  a  lateral  half  of  the  fornix. 
Along  the  concave  side  of    the  same  fissure    another  and 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.        211 

slighter  ridge  appears  which  is  the  primitive  tcenia  semi- 
circularis. 

Fusions. — The  hemisphere  vesicle  so  increases  in  size  by 
the  eighth  week  of  embryonic  life  as  to  come  in  contact  with 
its  fellow  of  the  opposite  side,  and  with  the  dorsal  and  lateral 
surfaces  of  the  thalamencephalon.  At  those  two  points  of 
contact  certain  fusions  occur: 

(1)  Fusion  of  the  Hemispheres  with  Each  Other. — The 
hemisphere  vesicles  touch  one  another  in  front  of  the  lamina 
terminalis.  The  area  of  contact  is  at  first  small  and  is 
crescentic  in  shape.  The  convexity  of  the  crescent  looks  for- 
ward and  its  horns  diverge  backward.  Along  the  borders 
of  this  crescent  the  two  hemispheres  grow  together.  The 
crescents  themselves,  remaining  free,  form  the  septum 
lucidum  and  inclose  between  them  the  fifth  ventricle.  First, 
ix  strong  round  bundle  of  fibers  is  thrown  across  at  the  ante- 
rior inferior  angle  of  the  crescent,  which  is  the  anterior  com- 
missure. Pressure  of  the  anterior  commissure  against  the 
lamina  terminalis  causes  the  latter  to  be  absorbed  back  to 
its  lining  epithelium.  That  epithelium  separates  the  com- 
missure from  the  third  ventricle  in  the  adult.  Second,  fusion 
occurs  along  the  concave  border  (the  postero-inferior)  of  the 
crescent.  That  border  coincides  with  the  fornix  ridge  above 
referred  to;  and  fusion  of  the  two  ridges  forms  the  lody  of 
the  fornix.  The  anterior  pillar  hooks  around  the  foramen  of 
Monro,  and  turns  back  into  the  lateral  wall  of  the  thalamen- 
cephalon; the  posterior  pillar  grows  backward  with  the 
hemisphere.  Certain  fibers  are  thrown  across  between  the 
posterior  pillars  to  form  the  commissura  hippocampi.  Last, 
fusion  occurs  along  the  convexity  of  the  crescent.  It  forms 
the  corpus  callosum.  The  rostrum  and  genu  are  first  de- 
veloped.    Like  the  fornix,  it  grows  with  the  hemispheres 


212  THE    BRAIN   AND    SPINAL   CORD. 

backward  until  completed.  With  the  development  of  tlie 
corpus  callosum  the  borders  of  the  crescentic  area  are  com- 
pletely fused  and  the  fifth  ventricle  inclosed. 

(2)  Fusion  of  the  Hemispheres  with  the  Thalamencephw- 
lon. — Fusion  occurs  between  the  hemisphere  vesicle  and  the 
lateral  surface  and  a  small  part  of  the  superior  surface  of  the 
thalamencephalon.  The  blending  of  the  medial  wall  of  the 
hemisphere  and  the  external  surface  of  the  thalamencephalon 
is  produced  by  the  growth  of  that  fan-shaped  group  of  fibers 
called  the  superior  lamina  of  the  internal  capsule.  The 
growth  of  the  fibers  which  form  the  internal  capsule  from  the 
cortex  downward  and  from  the  optic  thalamus  and  other 
ganglia  upward  is  the  cause  of  that  blending.  On  the  su- 
perior surface  of  the  thalamencephalon,  fusion  takes  place 
as  far  medialward  as  the  oblique  (choroid)  groove  on  the 
optic  thalamus  (which  see).  Here  the  hemisphere  wall  is 
represented  by  a  single  layer  of  epithelium,  which  invests  the 
optic  thalamus  on  the  superior  surface  external  to  the  choroid 
groove.  It  is  continuous  toward  the  median  line  with  the 
fold  inclosing  the  choroid  plexus ;  and  it  extends  between  the 
taenia  semicircularis  and  margin  of  the  fornix.  The  epithe- 
lium is  in  continuity  with  the  ependymal  lining  of  the  lateral 
ventricle. 

Velum  Interpositum. — The  growth  of  the  meninges  and 
brain  vesicles  occurs  pari  passu.  The  pia  mater  is  at  all 
times  in  contact  with  the' surface  of  the  vesicles;  and  it  gives 
off  branching  trabeculae  which  form  the  connective  tissue 
network  of  the  nerve  substance.  Wherever  fusion  between 
the  brain  vesicles  occurs,  the  two  layers  of  pia  are  absorbed; 
and  they  unite  with  one  another  just  beyond  the  line  of 
fusion.  Thus  the  pia  of  the  hemispheres  unites  above  the 
corpus  callpsuTO  and  beneath  thq  fornix,  when  those  connect- 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.        2I3 

JDg  links  are  formed  between  the  hemispheres.  The  pia  be- 
neath the  fornix  is,  therefore,  continuous  with  that  covering 
the  lower  half  of  the  medial  wall  of  each  hemisphere;  and, 
by  growth  of  the  hemispheres  and  fornix,  it  is  carried  back 
over  the  pia  investing  the  thalamencephalon.  Fusion  of  the 
thalamencephalon  with  each  hemisphere  causes  absorption  of 
the  double  layer  of  pia  mater  upward  to  the  choroid  groove 
on  the  thalamus  and  union  of  the  two  laminae  along  that 
groove.  The  result  is  a  triangular  sheet  made  up  of  two 
layers  of  pia,  the  velum  interpositum.  The  velum  inter- 
positum  separates  the  fornix  from  the  inter-brain  in  the  ma- 
ture organ.  Its  inferior  layer,  called  the  superior  choroid 
tela,  adheres  in  its  median  portion  to  the  roof  epithelium  of 
the  third  ventricle.  Two  longitudinal  folds  in  the  superior 
choroid  tela  constitute  the  choroid  plexuses  of  the  third  ven- 
tricle. The  borders  of  the  velum  form  the  choroid  ylexus 
of  each  lateral  ventricle. 

THALAMENCEPHALON. 

This  is  the  posterior  division  of  the  anterior  primary 
vesicle.  It  forms  the  Inter-Brain  and  the  Third  Ventricle, 
except  its  anterior  boundary.  Before  the  anterior  primary 
vesicle  is  divided  and  the  thalamencephalon  constricted  off 
from  the  prosencephalon,  the  Optic  Vesicle  makes  its  appear- 
ance on  either  side.  It  is  a  prominent  diverticulum  at  first ; 
but  it  grows,  in  man,  less  rapidly  than  the  vesicle  from  which 
it  rises.  The  optic  vesicle  becomes  cupped,  and  is  then  the 
primitive  retina.  From  it  the  optic  nerves  grow  back  to  the 
ventral  surface  of  the  thalamencephalon,  where  they  help  to 
form  the  optic  chiasma  and  tracts.  Later,  the  tracts  grow 
back  along  the  side  of  the  thalamencephalon,  and  become 
connected  with  the  external  geniculate  body,  optic  thalamus 
and  corpora  quadrigemina. 


214  THE    BRAIN   AND   SPINAL    CORD. 

The  Optic  Thalamus  is  formed  by  thickening  of  the  Lateral 
Wall  of  the  second  vesicle.  It  fuses  externally  with  the 
hemisphere  (corpus  striatum)  and  forms  the  superior  lamina 
of  the  internal  capsule.  Internally,  it  fuses  at  one  point 
with  its  fellow  of  the  opposite  side,  forming  the  middle 
commissure.  The  medial  surface  presents  a  longitudinal 
groove,  the  sulcus  of  Monro,  which  is  supposed  to  separate 
the  ventral  and  dorsal  zones  of  the  thalamencephalon.  A 
slight  thickening  of  the  postero-inferior  wall  of  the  thala- 
mencephalon is  the  primitive  external  geniculate  hody. 

From  the  floor  of  the  thalamencephalon  are  developed  the 
corpora  albicantia  (at  first  single) ;  the  tuber  cinereum  and 
infundibulum  and  the  lamina  cinerea. 

The  Superior  Wall,  or  Roof,  of  this  second  vesicle  stretches 
out  and  becomes  very  thin,  except  at  its  posterior  extremity, 
where  it  develops  a  transverse  white  band,  the  posterior  com- 
missure. Immediately  in  front  of  this  commissure,  a  divertic- 
ulum of  the  roof  appears  which  is  the  primitive  pineal  hody.. 
Two  longitudinal  folds  of  the  roof  dip  down  into  the 
ventricular  cavity.  These  are  followed  by  two  like  down- 
ward projecting  folds  from  the  inferior  lamina  of  the  velum 
interpositum,  which  constitute  the  choroid  plexuses  of  the 
third  ventricle. 

MESENCEPHALON. 

This  is  the  Embryonic  Mid-Brain.  It  is  the  third  of  the 
secondary  vesicles.  Tlie  elbow  of  the  mesencephalic  flexure 
of  180  degrees  is  formed  by  it;  and  that  flexure  almost 
brings  the  thalamencephalon  and  epencephalon  in  contact 
with  one  another  beneath  it.  The  mesencephalon  remains 
small,  but  its  walls  thicken  greatly.  As  a  result  of  the 
thickening,  its  cavity  is  reduced  to  a  slender  canal,  the 
aqueduct  of  Sylvius,  in  the  floor  of  which  develop  the  nuclei 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.        21 5 

of  the  third  and  fourth  pairs  of  cranial  nerves.  The  latter 
is  developed  in  the  constriction  (isthmus  of  His)  between  the 
third  and  fourth  brain  vesicles.  The  walls  of  the  mesen- 
cephalon form,  ventrally,  the  substantia  nigra  and  part  of  the 
tegmentum ;  and,  dorsally,  the  remainder  of  the  tegmentum. 
The  down-growth  of  the  motor  fibers  of  the  internal  capsule, 
along  the  ventral  surface  of  the  mesencephalon,  produces 
the  Uvo  crustce.  About  the  third  month  the  dorsal  thick- 
ening is  divided  by  a  fore  and  aft  groove,  the  sulcus 
longitudinalis.  A  transverse  groove  appears  two  months 
later  and  completes  the  crucial  groove  and  the  outline  of  the 
corpora  quadrigemina.  The  antero-lateral  part  of  the  roof 
forms  the  internal  geniculate  body.  By  the  growth  of  fibers 
which  connect  the  geniculate  bodies  with  the  corpora  quadr 
rigemina,  the  superior  and  inferior  brachia  are  formed. 

EPENCEPHALON. 

The  fourth  brain  vesicle  is  the  Kudimentary  Hind-Brain. 
It  forms  the  pons  and  cerebellum,  the  former  from  its  floor 
and  the  latter  from  its  roof.  Superiorly,  its  cavity  contracts 
to  the  size  of  the  Sylvian  aqueduct ;  it  expands  inf eriorly  and 
is  broadest  at  the  junction  of  the  pons  with  the  medulla 
oblongata.  The  ventricular  surface  presents  on  each  lateral 
wall  a  longitudinal  furrow  which  divides  the  epencephalon 
into  a  ventral  and  a  dorsal  zone.  The  ventral  zone  is  com- 
posed of  the  floor  and  ventro-lateral,  or  basal,  laminae,  and 
the  dorsal  zone  is  made  up  of  the  roof  and  dorso-lateral,  or 
alar,  laminae.  We  shall  find  this  division  continued  in  the 
metencephalon  and  the  spinal  part  of  the  neural  tube. 

Cerebellum. — A  long  transverse  thickening  may  be  ob- 
served in  the  superior  part  of  the  epencephalon-roof  as  early 
as  the  second  month.  The  inferior  part  of  the  roof  remains 
thin.     At  the  third  month  that  ridge  presents   a  median 


2l6  THE    BRAIN   AND    SPINAL    CORD. 

enlargement,  divided  by  three  transverse  fissures,  which  is 
the  embryonic  valve  of  Vietissens  and  vermis  cerehelli.  The 
lateral  portions  of  the  transverse  ridge  grow  rapidly  after  the 
third  month.  They  form  the  cerebellar  hemispheres.  At 
first  the  hemispheres  are  smooth,  but  they  become  lobulated 
about  the  fifth  month  and  foliated  a  month  later.  The  Cere- 
hellar  Peduncles  are  completed  at  the  same  time.  The  Infe- 
rior appear  first  and  produce  a  prominent  ridge  in  each  lateral 
wall  of  the  epenoephalon  at  the  third  month.  A  month  later 
the  middle  peduncles  are  formed  and  the  superior  are  com- 
pleted about  the  fifth  month.  The  peduncles  are  produced 
by  the  growth  of  axones  from  various  masses  of  neuroblasts. 
Pons. — The  pons  develops  simultaneously  with  the  cere- 
bellum. The  ventral  zone  of  the  epencephalon  thickens 
greatly.  The  neuroblasts  formed  therein  constitute  the 
nuclei  of  the  pons  and  of  the  reticular  formation,  and  the 
motor  nuclei  for  the  fifth,  sixth  and  seventh  pairs  of  cranial 
nerves;  the  dorsal  lamina,  in  the  lateral  wall  of  the  epen- 
cephalon, produces  the  neuroblasts  which  form  the  superior 
olivary  nucleus  and  the  superior  terminal  nucleus  of  the 
sensory  part  of  the  trifacial  nerve.  From  the  nucleus  pontis 
axones  ascend  through  the  lateral  walls  of  the  epencephalon 
to  the  cerebellum  and  others  descend  from  the  cerebellum 
by  the  same  course  to  the  pons.  They  form  the  middle  cere- 
hellar  peduncles.  At  the  same  time,  about  the  fourth  month, 
the  motor  tracts  composing  the  crustae  of  the  mid-brain  grow 
downward  into  the  ventral  portion  of  the  pons  and  the 
fronto-pontal,  temporo-pontal  and  intermediate  tracts  end  in 
the  nuclei  pontis.  The  pyramidal  fibers  to  motor  nuclei  of 
bvilbar  and  spinal  nerves  grow  down  through  the  pons,  inter- 
secting its  transverse  fibers. 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.        217 
METENCEPHALON. 

The  metencephalon  forms  the  Medulla.  Oblongata.  It  is 
constricted  off  from  the  epencephalon  at  the  twenty-eighth 
day;  but,  later,  that  constriction  largely  disappears  and  the 
common  cavity  of  the  two  vesicles,  broad  in  the  middle  and 
contracted  to  a  slender  canal  at  each  end,  persists  as  the 
fourth  ventricle  of  the  mature  brain.  Like  the  epencephalon, 
the  fifth  brain  vesicle  is  divided  at  the  third  week  into  a 
ventral  and  a  dorsal  zone  by  a  deep  furrow  on  the  ventricular 
surface  of  each  lateral  wall.  That  lateral  furrow,  as  regards 
position,  is  represented  in  the  mature  organ  by  the  dorso- 
lateral groove  on  the  exterior  surface  of  the  medulla  and  it 
actually  persists  in  the  superior  and  inferior  fovea  of  the 
fourth  ventricle.  The  anterior  and  lateral  columns  of  the 
medulla,  which  are  anterior  to  the  dorso-lateral  groove,  are 
therefore  developed  in  the  ventral  zone;  and  the  structures 
situated  behind  the  dorso-lateral  groove,  namely,  the  poste- 
rior columns,  the  restiform  bodies  and  the  roof  epithelium, 
are  formed  in  the  dorsal  zone. 

The  roof  of  the  superior  half  of  the  metencephalon 
stretches  out  widely  and  remains  a  single  layer  of  epithelial 
cells.  It  forms  no  nerve  tissue.  Other  portions,  of  the 
metencephalon  develop  quite  uniformly.  But  by  the  expan- 
sion of  the  roof,  just  mentioned,  the  dorsal  extremities  of 
the  lateral  walls  are  pushed  outward  and  forward  almost  to 
the  plane  of  the  floor,  and  a  transverse  section  of  the  vesicle 
in  that  region  presents  the  form  of  a  very  broad  capital  V 
with  the  roof  epithelium  stretching  between  the  two  arms 
and  converting  the  letter  into  a  triangle.  Transverse  sec- 
tion through  the  lower  half  of  the  metencephalon  at  the  third 
or  fourth  week  shows  an  elongated  ellipse  with  a  dorse-ven- 
tral major  axis. 


2l8  THE    BRAIN   AND   SPINAL    CORD. 

Internal  Surface. — The  lateral  wall,  in  both  upper  and 
lower  regions,  presents  the  longitudinal  groove  which  sepa- 
rates the  ventral  and  dorsal  zones.  The  median  ventral 
groove  persists  throughout  and  the  lateral  grooves  are  repre- 
sented by  the  fovea,  of  the  fourth  ventricle.  The  low  emi- 
nence situated  between  the  median  and  each  lateral  groove 
becomes  the  fasciculus  teres. 

External  Surface. — On  the  external  surface  of  the  meten- 
cephalon  and  along  the  ventral  border  of  the  dorsal  zone, 
there  appears  very  early  an  oval  bundle  of  descending  fibers, 
called  the  solitary  bundle.  It  is  composed  of  axones  from 
the  jugular  and  petrosal  ganglia,  and  constitutes  the  descend- 
ing root-fibers  of  the  ninth  and  tenth  pairs  of  nerves.  At 
about  the  same  time  axones  from  the  Gasserian  ganglion 
form  a  bundle  of  descending  fibers  on  the  lateral  surface 
dorsal  to  the  solitary  bundle.  They  constitute  the  so-called 
ascending  root  of  the  trifacial  nerve.  Soon  after  the  ap- 
pearance of  the  solitary  bundle  and  the  "ascending"  root  of 
the  fifth  nerve,  the  posterior  margin  of  the  dorso-lateral 
lamina  is  folded  outward  and  forward  until  it  rests  upon 
the  external  surface  of  the  ventro-lateral  lamina.  That 
fold  covers  both  the  above  bundles  of  fibers  and  places  them 
in  the  position  they  occupy  in  the  mature  brain. 

The  Substance  of  the  Metencephalon,  like  other  divisions 
of  the  neural  tube,  presents,  under  the  microscope,  three  dis- 
tinct zones  at  the  fourth  week  of  embryonic  life.  The  outer 
layer  is  composed  of  neuroglia;  the  middle,  or  mantle,  layer 
of  neuroblasts ;  and  the  inner,  or  ependymal,  layer  is  made 
up  of  columnar  epithelial  cells.. 

The  Cells  of  the  Inner  Layer  become  ciliated  and  form  the 
lining  of  the  ventricle. 

The  Mantle,  or  Middle,  Layer  undergoes  most  develop- 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.       2I9 

ment.  Its  neuroblasts  form  the  formatio  reticularis  and  the 
cranial  nerve  ajid  other  nuclei  of  the  medulla  oblongata.  In 
the  dorsal  zone  the  neuroblasts  form  the  terminal  nuclei  for 
the  eighth,  ninth  and  tenth  cranial  nerves  and  the  nucleus 
gracilis,  nucleus  cuneatus  and  nucleus  of  Rolando.  As  early 
as  the  fourth  week  axones  may  be  traced  from  the  last  three 
nuclei,  ventro-medially,  toward  the  point  where  they  very 
soon  form  the  sensory,  or  -fillet,  decussation.  Neuroblasts 
which  have  wandered  from  the  dorsal  zone  form  the  olivary 
and  accessory  olivary  nuclei  quite  late  in  intra-uterine  life 
(6th  month).  From  the  neuroblasts  of  the  ventral  zone  are 
developed  the  gray  matter  and  fibers  of  the  formatio  reticu- 
laris alba  et  grisea,  and  the  motor  nuclei  of  the  twelfth, 
eleventh  (accessory  part),  tenth  and  ninth  pairs  of  cranial 
nerves. 

The  Neuroglia  Layer  forms  the  supporting  matrix  for  the 
tracts  of  fibers,  and  the  raphe  of  the  medulla.  By  the  third 
month  the  fasciculus  gracilis,  fasciculus  cuneatus  and  fascic- 
ulus of  Eolando,  extensions  of  GolFs  and  Burdach's  col- 
umns in  the  cord,  have  grown  up  to  their  terminal  nuclei 
in  the  medulla.  The  restiform  body  is  at  that  time  well  de- 
veloped, and  the  tracts  of  the  lateral  area  of  the  medulla  are 
visible.  The  posterior  longitudinal  bundles  appear  near  the 
median  raphe  in  the  ventral  zone  at  about  the  same  time ;  and, 
ventral  to  them,  fibers  from  the  sensory  decussation  form  the 
inter  olivary  fillets.  The  great  motor  tracts  from  the  Eo- 
landic  area  of  the  cortex  reach  the  medulla  at  the  fourth 
month.  G-rowing  downward,  on  either  side  of  the  median 
line,  they  conceal  the  interolivary  fillets  and  form  the  pyra- 
mids of  the  medulla  oblongata.  The  form  of  the  medulla 
is  completed  two  months  later  (the  6th  month)  by  the  ap- 
pearance of  the  olivary  bodies. 


220  THE    BRAIN   AND   SPINAL   CORD. 

SPINAL    CORD. 

That  portion  of  the  neural  tube  which  is  situated  behind 
the  metencephalon  is  the  embryonic  spinal  cord.  It  is  of 
nearly  uniform  size  from  cephalic  to  caudal  end.  Inferiorly, 
it  is  open  into  the  alimentary  canal  for  a  short  time.  The 
lumen  of  the  neural  tube  is  at  first  large  and  elliptical  in 
shape.  Later,  at  the  sixth  week,  it  has  a  diamond  shape,  the 
acute  angles  of  the  diamond  being  formed  by  the  roof  and 
floor  of  the  canal,  and  it  is  lined  with  columnar  ciliated  cells. 
As  the  walls  thicken  the  canal  is  contracted  more  and  more 
until  it  reaches  the  capillary  size  of  the  adult  cord.  It  is 
continuous  with  the  fourth  ventricle  above  and  dilates  to 
form  the  inferior  rhomboid  fossa  in  the  filum  terminale.  The 
neural  tube  forms  the  whole  substance  of  the  spinal  cord, 
with  the  exception  of  the  great  motor  tracts  that  grow  into  it 
from  the  brain,  and  the  sensory  tracts  and  fibers  that  enter  it 
from  the  spinal  and  sympathetic  ganglia.  At  the  sixth  week 
of  embryonic  life  the  anterior  and  posterior  roots  of  the 
spinal  nerves  are  clearly  seen;  they  are  horizontal  in  direc- 
tion. The  cord  extends  the  entire  length  of  the  spinal  canal 
until  the  third  month,  when  the  caudal  end  begins  to  recede. 
It  reaches  only  to  the  third  lumbar  vertebra  at  birth  and, 
in  the  adult,  but  to  the  lower  border  of  the  first  lumbar 
vertebra.  With  the  rapid  growth  of  the  spinal  column,  the 
roots  of  the  lumbar,  sacral  and  coccygeal  nerves  become 
greatly  elongated  and,  together  with  the  filum  terminale, 
form  the  cauda  equina.  Meninges. — The  investing  meso- 
blast  of  the  neural  tube  develops  the  meninges  of  the  spinal 
cord. 

Zones. — By  the  sixth  week  of  intra-uterine  life  the  neural 
tube  is  divided  into  a  ventral  and  a  dorsal  zone  by  a  lateral 
groove   on   either   side   continuous   with   those   dividing  the 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.       221 

metencephalon  and  epencephalon.  The  tube  presents  ex- 
ternally, opposite  to  each  lateral  groove,  a  furrow  called  th^' 
central  fissure,  which  is  occupied  later  by  the  crossed  pyram 
idal  tract.  The  whole  of  the  spinal  cord  anterior  (or  ven- 
tral) to  the  cervices  of  the  posterior  comua  of  gray  matter 
is  represented  by  the  ventral  zone.  In  the  dorsal  zone,  the 
heads  of  the  posterior  cornua  and  the  posterior  columns  are 
developed.  The  cervix  of  each  posterior  horn  is  formed  by 
the  thin  lamina  connecting  the  two  zones. 

Three  Histologic  Layers. — At  a  time  somewhat  earlier 
than  the  division  into  ventral  and  dorsal  zones,  even  at  the 
fourth  or  fifth  week,  the  spinal  part  of  the  neural  tube  pre- 
sents three  microscopic  layers,  like  those  seen  earlier  in  the 
metencephalon  and  other  brain  vesicles. 

The  Outer  Layer,  composed  of  neuroglia,  is  very  thin  except 
in  the  floor  of  the  tube  on  either  side  of  the  median  line; 
and  later,  in  the  corresponding  parts  of  the  roof.  In  those 
situations  are  formed  the  anterior  and  posterior  columns  of 
the  cord.  The  central  fissure  (see  above),  also,  presents  a 
thickening  of  neuroglia  through  which  grow  the  crossed 
pyramidal  and  direct  cerebellar  tracts. 

The  Second  Layer  is  gray  matter.  It  is  the  mantle  layer 
and  contains  the  neuroblasts.  At  the  fourth  or  sixth  week 
it  is  very  thick,  comprising  nearly  all  of  the  neural  tube. 
The  H-shaped  column  of  gray  substance  is  derived  from  this 
layer.  In  the  ventral  zone  the  neuroblasts  collect  near  the 
floor  of  the  tube  and  form  a  large  column  on  either  side  of 
the  median  line.  The  axones  of  the  more  ventrally  located 
neuroblasts,  anterior  cornua,  grow  centrifugally  out  of  the 
antero-lateral  surface  of  the  neural  tube.  They  form  the 
anterior  roots  of  the  spinal  nerve-s.  The  more  dorsally  lo- 
cated neuroblasts  develop  axones  also;  but  on  account  of 


222  THE    BRAIN    AND    SPINAL    CORD. 

meeting  resistance,  according  to  His,  they  become  longi- 
tudinal and  form  the  ground  bundles  of  the  cord  and  the 
ant ero -lateral  ascending  cerebellar  and  direct  cerebellar 
tracts.  The  gray  matter  in  the  dorsal  zone  becomes  trans- 
formed into  the  heads  of  the  posterior  cornua;  its  neuro- 
blasts form  only  intrinsic  neurones,  their  processes  remain- 
ing in  the  spinal  cord.  Axones  from  the  spinal  ganglia, 
forming  the  posterior  roots  of  the  spinal  nerves,  grow  into 
the  dorsal  zone;  and  each  axone  divides  T-like  into  a  small 
descending  and  a  large  ascending  branch,  and  also  gives 
off  many  collaterals  both  before  and  after  division.  The 
ascending  fibers  for  a  time  form  the  oval  bundle  of  His  on  the 
surface  of  the  tube;  later,  they  constitute  the  tract  of  Lis- 
sauer,  most  of  Burdach's  and  all  of  GolPs  columns. 

The  Third  Layer,  the  ependymal  layer,  lines  the  ventricle. 
It  is  composed  of  neuroglia  covered,  internally,  by  columnar 
ciliated  cells,  which  appear  about  the  fifth  week. 

The  Longitudinal  Tracts. — The  white  columns  of  the  spi- 
nal cord  are  formed  in  the  superficial,  or  neurogliar,  layer. 
At  first  they  are  composed  of  non-medullated  fibers,  and  it  is 
a  remarkable  fact  that  the  various  tracts  receive  their 
myeline  sheaths  at  definite  periods  between  the  fifth  and 
ninth  months  of  intra-uterine  life  (Flechsig).  The  ground 
bundles  and  the  posterior  columns  first  appear.  They  may  be 
seen  at  the  sixth  week.  The  ascending  cerebellar  tracts  fol- 
low. And  the  descending  cerebellar  and  the  direct  and 
crossed  pyramidal  tracts  are  last  to  appear;  they  are  not  de- 
veloped before  the  fourth  or  fifth  month.  According  to 
Flechsig,  the  tracts  of  the  spinal  cord  are  medullated  as  fol- 
lows : 

1.  The  ground  bundles  of  the  posterior  columns  at  about 
the  fifth  month. 


EMBRYOLOGY    OF    THE    BRAIN    AND    SPINAL    CORD.       223 

2.  The  ground  bundles  of  the  anterior  columns  about  the 
sixth  month. 

3.  The  ground  bundles  of  the  lateral  columns  from  the 
fifth  to  the  seventh  month  (antero-lateral,  mixed  column 
fifth  to  seventh  month,  and  lateral  limiting  layer,  sixth 
month) . 

4.  The  columns  of  Goll  ajid  Burdach  (excepting  ground 
bundles)  between  the  sixth  and  seventh  months. 

5.  The  direct  cerebellar  tract  at  the  seventh  month. 

6.  The  antero-lateral  cerebellar  tracts,  ascending  and  de- 
scending, at  the  eighth  month. 

7.  The  direct  and  crossed  pyramidal  tracts  at  the  ninth 
month. 

Fissures. — The  so-called  Posterior  Median  Fissure  is  in 
reality  a  septum  of  neuroglia.  At  no  time  is  it  a  true  fis- 
sure. It  appears  to  be  formed  by  the  approximation  of  the 
lateral  walls  of  the  neural  canal.  After  the  sixth  week  the 
approximation  begins  at  the  roof  and  gradually  proceeds 
ventrally  to  the  center  of  the  cord.  The  ependyma  which 
originally  lined  the  dorsal  part  of  the  canal  is  thus  fused 
into  the  posterior  median  septum  of  neuroglia. 

The  Poster o-lateral  Fissure  is  the  groove  between  the  lat- 
eral border  of  the  posterior  column  and  the  dorsal  border  of 
the  lateral  column.  It  is  the  development  of  the  posterior 
and  lateral  columns  that  produces  this  fissure.  The  em- 
bryonic central  fissure  is  obliterated  and  the  postero-lateral 
surface  of  the  cord  rendered  prominent  by  the  formation  of 
the  direct  cerebellar  and  crossed  pyramidal  tracts. 

Anterior  Median  Fissure. — That  is  a  true  fissure.  It  be- 
gins to  be  formed  at  the  sixth  week,  when  the  earliest  fibers 
of  the  antero-lateral  ground  bundle  are  developed.  It  deep- 
ens with  the  growth  of  the  antero-lateral  ground  bundle  and 


224  THE    BRAIN    AND   SPINAL    CORD. 

is  completed,  in  the  fourth  or  fifth  month,  by  the  descent  of 
the  direct  pyramidal  tract.  Those  two  tracts  cause  a  bulg- 
ing in  the  ventral  surface  on  either  side  of  the  median  line 
which  increases  with  the  medullation  of  the  pyramidal  tracts 
in  the  ninth  month ;  and  the  ridges  thus  produced,  failing  to 
fuse  completely,  become  the  walls  of  the  anterior  median 
fissure.  The  partial  fusion  which  does  occur  between  the 
two  ridges  is  due  to  the  formation  of  the  anterior  commis- 
sure of  the  cord. 


ADDENDA 


Note  1.  The  fibers  of  the  stria  medullaris  terminate  in  the  nucleus 
of  the  habenula  on  both  sides  of  the  median  line;  those  crossing  over 
run  through  the  dorsal  lamina  of  the  pineal  stalk  and  form  the  com- 
missura  habenularum   (page  46). 

Note  2.  Terminations  of  dendrites.  (1)  They  may  form  synapses 
with  other  neurones;  (2)  They  may  end  in  free  beaded  points  among 
the  cells  near  a  surface,  or  (3)  They  may  end  within  special  end 
organs,  such  as  Kraus',  Vater's,  Meissner's  Ruffini's  and  the  Neuro- 
tendinous and  Neuro-muscular  spindles  (page  67). 

Note  3.  There  are  three  varieties  of  neuroglia  cells,  viz.:  (1) 
The  short  rayed  cells,  found  in  the  cortex  of  cerebellum  and  cere- 
brum, the  processes  of  which  are  strong  and  richly  branched.  (2) 
The  long  rayed  cells,  located  chiefly  in  the  white  substance,  whose 
processes  a.re  long  and  fine  and  but  little  branched'.  And  (3)  the 
arborescent  cells  which  lie  near  the  surface  in  the  cortex.  Upon 
reaching  the  surface  the  tree-like  branches  form  a  limiting  mepi- 
brane  of  neuroglia  (p.  67). 

Note  4.  The  first  layer  of  cerebral  cortex  contains  a  rich  tan- 
gential network  associative  in  function  which,  according  to  Cunning- 
ham, bears  a  direct  relation  to  intellectuality.  The  network  is  made 
up  of  the  processes  of  Cajal's  cells,  of  the  pyramids'  dendrites,  of 
axones  from  Martinotti's  cells,  and  of  other  corticipital  fibers  which 
belong  to  the  associative,  the  commissural  and  the  afferent  projection 
systems  (page  72). 

Note  5.  The  dendrites  of  the  polymorphous  cells  in  the  fourth 
layer  of  cerebral  cortex  branch  very  richly  in  the  deeper  layers,  but 
fail  to  reach  beyond  the  pyramids.  Those  derived  from  Martinotti's 
cells  ramify  toward  the  white  substance,  while  the  axones  of  the 
same  cells  enter  into  the  tangential  network  of  the  first  cortical 
layer. 

The  distinction  between  fourth  and  fifth  layers  is  not  very  clear 
and,  accordingly,  Cajal  describes  them  together  as  the  polymorphous 
layer  (page  74). 

Note  6.  Two  varieties  of  cells  are  found  in  the  cerebral  cortex 
which  differ  somewhat  from  those  forming  the  typical  layers.  They 
are  the  dendraxones  of  Golgi  and  the  inverted  pyramids  of  Marti- 
notti  situated  in  the  deep  part  of  the  cortex  among  the  pyramids  and 
polymorphous  cell-bodies. 

Golgi's  cell  appears  to  be  associative  in  function,  as  both  axones 
and  dendrites  terminate  by  multiple  division  in  the  immediate  vicin- 
ity of  the  cell-body;  neither  reaches  as  far  as  the  white  substance  of 
the  hemisphere  or  the   superficial  layer  of  cortex. 

Martinotti's  cell  is  small  and  somewhat  irregular  in  shape,  but 
often  resembles  an   inverted  pyramid.     Its  dendrites  arborize  toward 


226  ADDENDA. 

but  not  into  the  white  substance.  It  possesses  a  single  axone  which 
runs  out  to  the  neurogliar  layer,  where  its  T-branches  and  collaterals 
enter  into  the  tangential  network  (page  74). 

Note  7.  The  cerebral  commissures  are  the  corpus  callosum;  ante- 
rior, middle  and  .posterior  commissures;  commissura  hippocampi; 
commissura  habenularum:  and  Gudden's  and  Meynert's  commis- 
sures (page  91). 

Note  8.  The  T-branches  of  the  cerebellar  granules  run  parallel 
with  the  intralobular  fissures  and  pierce  the  dendritic  planes  of  Pur- 
kinje's  cells. 

A  thin  layer  of  large  granules  is  found  next  the  bodies  of  Pur- 
kinje's  cells.  The  axones  of  these  large  granules  arborize  within  the 
granular  layer  toward  the  white  substance  and  their  dendrites  ram- 
ify richly  in  the  superficial  layer.  The  large  granules  belong  to  the 
type  of  Golgi  and  are  associative  in  function  (page  113). 

Note  9.  The  antero-lateral  ascending  cerebellar  tract  (Gowers') 
in  the  pons  is  found  scattered  in  that  part  of  the  formatio  reticularis 
which  is  lateral  to  the  root  of  the  abducent  nerve,  being  continued 
from  the  formatio  reticularis  grisea  of  the  medulla  oblongata  (page 
123). 

Note  10.  Not  all  axones  of  the  superior  olivary  nucleus  enter  the 
lateral  fillet;  a  small  number,  constituting  the  stalk  of  the  superior 
olive,  run  directly  to  the  abducent  nucleus,  and  others  join  the  poste- 
rior longitudinal  bundle  and  run  to  the  nuclei  of  the  trochlear  and 
oculomotor  nerves.  In  this  manner  there  is  formed  the  middle  link  of 
an  auditory-ocular  reflex  arc  (page  126). 

Note  11.  Fibers  from  nuclei  of  the  formatio  reticularis  in  the 
pons  and  medulla,  from  Deiter's  nucleus  and  from  Flechsig  and  Bech- 
terew's  nucleus  probably  join  the  cerebellar  fibers  in  making  up  the 
antero-lateral  descending  cerebellar  tract  as  described  in  this  work 
(pages  141,   144,   174). 

Note  12.  The  real  origin  of  sensory  nerves  is  found  to  be  in  their 
ganglia  external  to  the  brain  and  spinal  cord.  From  the  ganglion 
cells  the  dendrites  run  toward  the  periphery,  constituting  the  sensory 
nerves;  and  the  axones,  which  form  the  sensory  roots,  running  cen- 
trally, plunge  into  the  brain  or  cord  and  end  in  the  terminal  nuclei  of 
the  respective  nerves  (page  154). 

Note  13.  The  cornu  commissural  tract  is  an  ascending  tract, 
according  to  Morris,  but  Hoche  studied  two  cases  of  compression 
myelitis  in  which  the  degeneration  was  descending  in  this  tract 
(page  178). 

Note  14.  A  small  bundle  of  axones  from  the  corpus  albicans 
descends  along  the  floor  of  the  third  ventricle  to  the  tegmentum  of 
the  mid-brain,  but  its  destination  is  unknown   (Cunningham). 

Note  15.  E.  A.  Schaefer  has  demonstrated  that  the  fibers  of  the 
pyramidal  tracts  end  in  Clark's  column  and  about  the  cells  in  the 
posterior  horn  of  gray  matter  of  the  spinal  cord,  hence  one  or  more 
neurones  intervene  between  the  pyramidal  fibers  and  the  large  cell- 
bodies  in  the  anterior  horns. 


INDEX. 


A 

PAGE. 

Abducens  nerve 129,  140,  155 

Accessory  nucleus  cuneatus 143,  147 

Accessory  nucleus  of  ninth  and  tenth  cranial  nerves 152 

Accessory  sensory  roots  of  ninth  and  tenth  cranial  nerves 145 

Acervulus  cerebri 46 

Acustic  area 153 

Acustico-cerebellar  tract 114 

Acustic  radiations 26,  51,  63,  81,  90,  122 

Acustic  striae 151 

Acustic  trigone 151,  153 

Acustic  tubercle 153 

Afferent,  or  sensory,  conduction  paths 190-197 

After-brain,  or  medulla  oblongata 7, 128-149 

Alae  cerebelli 105 

Ala  cinerea ,   152 

Alar  lamina  (or  dorso-lateral) 215 

Alveus  of  hippocampus 41,    75 

Amygdala 25,  26,  37,    40 

Anastamotic  vein  of  Trolard 99 

Angular  convolution 12 

Annectant  convolutions 14 

Anosmia 75 

Ansa  lenticularis 56,  77,  80,  84,    89 

Ansa  peduncularis 26,  56,  79,    89 

Anterior  association  center 71 

Anterior  brachium 51,  59,  82,  215 

Anterior  cerebellar  notch 101 

Anterior  cerebral  arteries 95,    96 

Anterior  choroid  tela .- 5,  44,  46,  213 

Anterior  communicating  arteries 95 


INDEX. 

PAGE. 

Anterior  choroid  artery 117 

Anterior  commissure  of  cerebrum 7,  31,  43,  47,  211 

Anterior  commissure  of  cord 165,  171,  172,  224 

Anterior  cornu 166,  168 

Anterior  cornu  of  lateral  ventricle 38 

Anterior  crescentic  lobules  of  cerebellum 106 

Anterior  external  arciform  fibers 130,  131 

Anterior  great  transverse  fissure  (or  choroid) 213 

Anterior  horn  of  gray  matter •. 146 

Anterior  inferior  cerebellar  artery 117 

Anterior  longitudinal  bundle. . . .' 62,  82,  88, 124,  140,  173,  174 

Anterior  median  fissure  of  cord 163,  164,  223 

Anterior  median  fissure  of  medulla 128 

Anterior  nucleus  of  optic  thalamus 78 

Anterior  olfactory  lobule 22 

Anterior  orbital  convolutions 22 

Anterior  perforated  lamina 22 

Anterior  pillars  of  fornix 43,  44,  48,    79 

Anterior  quadrigeminal  body " 76,    82 

Anterior  root  of  spinal  nerves 180 

Anterior  segment  of  internal  capsule 27 

Anterior  spinal  artery 161,  182,  183 

Anterior  stalk  of  thalamus 28,  49,  80,    90 

Anterior  tubercle  of  optic  thalamus 50 

Anterior  white  column  of  cord " 167 

Anterolateral  ascending  cerebellar  tract  . .  .115,  131,140-142,  170,  174 

Anterolateral  descending  cerebellar  tract 

116,  131,  132, 140, 141, 144, 168,  174 

Antero-lateral  fissure  of  cord 164,  165 

Antero-lateral  ganglionic  arteries 96 

Antero-lateral  ground  bundle 131, 140,  141,  173,  174 

Antero-median  ganglionic  arteries 96 

Apertura  mediana  ventriculi  quarti 5,  133 

Aperturae  laterales  ventriculi  quarti 5,  133 

Apex  columnae  posterioris 169 

Apex  cornu  posterioris 169 

Apparent  central  termination  of  posterior  spinal  roots 181 

Aqueduct  of  Sylvius, 42,  43,  44.  58,  150,  214 


INDEX. 

PAGE. 

Arachnoid  of  brain 4 

Arachnoid  of  spinal  cord 160 

Arachnoidea  encephali 4 

Arachnoidea  spinalis 160 

Arbor  vitae 114 

Arciform   fibers 116,  132,  135,  144,  147,  178 

Arciform  nucleus 149 

Arcuate  association  fibers  of  cerebrum 91 

Area  acustica 153 

Area  of  Broca 22 

Area  of  cerebral  softening 97 

Area  of  general  sensation 13 

Area  parolfactoria  (Broca) 24 

Areas  of  medulla 136,  137 

Arteria  basilaris , 96 

Arteria  cerebri  anterior 95 

Arteria  cerebri  media 95 

Arteria  cerebri  posterior 96 

Arteria  choroidea  anterior 38,    97 

Arteria  choroidea  postero-lateralis 97 

Arteria  choroidea  postero-medialis 98 

Arteria  communicans  anterior 95 

Arteria  communicans  posterior 95 

Arteria  meningea  media 3 

Arteria  spinalis  anterior 161,  182 

Arteria  spinalis  posterior ; 161,  182 

Arteriae  choroideae 97 

Arteries  of  dura  mater 3 

Arteries  of  pia  mater 6 

Artery  of  cerebral  hemorrhage 97 

Ascending  frontal  convolution 11 

Ascending  parietal  convolution 11,     12 

Ascending  tracts  of  spinal  cord ; 172 

Association  fibers  of  cerebrum '. 85,  91-94 

Association  fibers  of  cerebellum 117 

Auditory  center  (sensory) 71 

Auditory  conduction  paths 63,  83,  90,  122,  195-197 

Auditory  cortex 26,    93 

111 


INDEX.       . 

PAGE. 

Auditory  lobes 83 

Auditory  memories 71,    93 

Auditory  nerves 137,  144 

Auditory  radiations  (see  acustic  radiations). 

Auditory  reflex 200 

Aula  of  third  ventricle 34,    42 

Axones  (or  neuraxanes) 66,    67 

B 

Basal  lamina  (ventro-lateral) 215 

Basal  or  inferior  surface  of  cerebrum 17,    24 

Basis  (es)  pedunculi  cerebri 7,  20,  25,  33,  53,    54 

Basket  cells  of  cerebellum 112 

Biventral  lobule 1 10 

Blood  supply  of  cerebrum  and  midbrain 94-99 

Blood  supply  of  cerebellum 117 

Blood  supply  of  pons 127 

Blood  supply  of  medulla  oblongata 158 

Blood  supply  of  spinal  cord 182-184 

Body  of  lateral  ventricle 35 

Borders  of  corpus  callosum 29 

Boundaries  of  fourth  ventricle 150 

Brachia  pontis 103,  115,  119,  121 

Brachmm  conjunctivum 64,  102,  115, 120,  127,  150 

Brachium  posterioris 122 

Brachium  quadrigeminum  inferioris 60 

Brachium  quadrigeminum  superioris 59 

Brain  sand 146 

Brain  vesicles  and  derivatives 207,  208 

Bulb  of  caudate  nucleus 37 

Bulbus  olfactorius 22,  122 

Burdach's  column 177,  178 

C  ^ 

Calamus  scriptorius 103,  145 

Calcar  avis 39 

Calcarine  fissure .' -    15 

Calloso-marginal  fissure . 14 

IV 


INDEX. 

PAGB. 

Canalis  centralis  spinalis 163 

Capsula  externa 25 

Capsula  interna 25,  26,  28,  31,  35,  36,  53,  54,  55,  211 

Caput  columnae  posterioris 169 

Caput  cornu  posterioris.  169 

Caput  nuclei  caudati 37 

Cardio-accelerator  center 168 

Cauda  equina 161 

Cauda  nuclei  caudati  37 

Caudate  nucleus 25,31,35.39,40,    76 

Cavernous  sinus 3 

Cavum  septi  pellucidi 34 

Cavum  subarachnoidiale 5 

Cavum  anterius  and  posterius .....   160 

Cells  of  anterior  cornu  of  spinal  cord 167 

Cells  of  Max  Schultze 23 

Cells  of  posterior  cornu 169,  170 

Cells  of  Purkinje Ill 

Center  of  gray  crescent  of  spinal  cord 167 

Center  of  hearing 14,     71 

Center  of  taste,  smell,  hearing 13,    71 

Center  of  vision 8,    71 

Central  canal  of  spinal  cord 150,  163 

Central  fissure  (of  cerebrum) 10 

Central  fissure  (embryonic  cord) 221 

Central  ligament  of  spinal  cord 161 

Central  lobe 14 

Central  lobule  and  alae  of  cerebellum. 105 

Central  nucleus  of  thalamus 79 

Central,  or  ventricular,  gray  matter  of  cerebrum 70,  84,    85 

Centrifugal  arteries  of  cord 183 

Centrifugal  fibers  of  corpus  sjtriatum 77 

Centrifugal  projection  fibers  of  cerebrum 85-89 

Centripetal  arteries  of  cord 183 

Centripetal  fibers  of  corpus  striatum.      ; 77 

Centripetal  projection  fibers  of  cerebrum 89-91 

Cerebellar  hemispheres 100 

Cerebellar  notches 101 


INDEX. 

PAGE. 

Cerebello-olivary  tract 116,  132,  136,  144,  148 

Cerebral  hemispheres 7,      8 

Cerebellum 7,  100-118 

Cerebro-corticopontal  paths 186,  187 

Cerebro-corticopontal  tracts,  frontal 56,    85 

Cerebro-corticopontal  tracts,  temporal , .55,    85 

Cerebrum 7-99 

Cervical  enlargement  of  spinal  cord 163 

Cervix  volumnae  posterioris 169 

Cervix  cornu  posterioris 169 

Chapter  1 1-8 

Chapter  II 9-51 

Chapter  III 51-65 

Chapter  IV 66-99 

Chapter  V 100-127 

Chapter  VI 127-149 

Chapter  VII 150-158 

Chapter  VIII 159-161 

Chapter  IX 162-184 

Chapter  X 185-200 

Chapter  XI 201-224 

Charcot's  artery 97 

Choroid  arteries 97,  98 

Choroid  fissure 2,  9,  10,  15,  41,  213 

Choroid  groove  of  thalamus 49,  212 

Choroid  plexus  of  fourth  ventricle 1 33,  151 

Choroid  plexus  of  lateral  ventricle 35,  38,  40,  46,  213 

Choroid  plexus  of  third  ventricle 43,  45,  48,  213,  214 

Choroid  vein 38,    98 

Cilio-spinal  center 168 

Cingulum 92 

Circle  of  Willis 94 

Circular  sinus 3 

Circulus  arteriosus 94 

Cisterna  cerebello-medullaris 5 

Cisterna  chiasmatis 5 

Cisterna  interpeduncularis 5 

Cisterna  pontis 5 

VI 


INDEX. 

PAGE. 

Clark's  column  of  cells 168 

Claustrum 25,    76 

Clava : 133, 143,  147 

Clivus  and  posterior  crescentic  lobules 106 

Cochlear  nucleus  (i) 63,  144,  153 

Collateral   fissure. . . .-. 16 

Colliculi  of  corpora  quadrigemina 54,  59,  82,    83 

Colliculus  facialis 102 

Columna  (ae)  anterior  in  medulla 146 

Columna  (ae )  in  spinal  cord 165,  166 

Columna  (fe)  fornicis 32 

Columna  (ae)  lateralis 166 

Columna  (ae)  posterior  in  medulla 147 

Columna  (ae)  in  spinal  cord 165,  166,  169 

Column  of  Clark " : 168,  169 

Column  of  Burdach 177,  178 

Column  of  Goll 179 

Column  of  Cowers 175 

Column  of  Loewenthal 175 

Column  of  Turck 174 

Column  of  Waldeyer 168 

Comma  tract 170,  178 

Commissura  anterior  alba 165,  167,  171,  172 

Commissura  anterior  cerebri 47 

Commissura  hippocampi 7,  32,  91,  211 

Commissural  fibers  of  cerebellum 116 

Commissural  fibers  of  cerebrum ........  85,    91 

Commissure  of  Gudden .• 20,    51 

Commissure  of  Meynert 81 

Conduction  paths , 185-201 

through  antero-lateral  ascending  cerebellar  tract ,  192,  193 

antero-lateral  ground  bundle  and  formatio  reticularis. . .   193 

cerebro-corticopontal  tracts 186,  187 

cochlear  nerve 195 

columns  of  Goll  and  Burdach. 190,  191 

cranial  nerves  and  medial  fillet 191 

direct  cerebellar  tract 191,  192 

formatio  reticularis 189,  190 

VII 


INDEX. 

PAGE. 

intermediate  bundle  of  crusta 187,  188 

ninth  nerve  and  corda  tympani 197 

olfactory  nerves,  tract,  &c 194 

optic  nerves,  tract,  &c 194,  195 

pyramidal  tracts 185,  186 

red  nucleus 188 

vestibular  nerve 196,  197 

Confluens  sinuum 2 

Conjugate  deviation 127,  189 

Connective  tissue  of  brain  and  cord 76 

Conus  medullaris 163 

Conus  terminalis 163 

Convolutions  or  gyri 9 

Cornu  ammonis  (hippocampus  major) , 73 

Cornu  commissural  tract 170,  178 

Cornua  of  lateral  ventricle 38-42 

anterior 38,    39 

middle 39-42 

posterior 39 

Cornu  (a)  ventriculi  lateralis 39-42 

anterius 38,39 

inferius 39-42 

posterius 39 

Corono  radiata 28 

Corpus  (ora)  albicans  (antia) 7, 18, 19,  33,  44,  57,  214 

callosum ^ 7,  8,  28,  30,  35,  39,  91,  211,  212 

dentatum  (a) 113 

fimbriatum  (a) 40 

fornicis 32,    92 

geniculatum  laterale 51,    82 

geniculatum  mediale 51,  60,    82 

mamillare   (ia) 19 

medullare  (cerebelli) 101,  114 

pineale 45 

quadrigeminum  (a) 7,  31,  51,  54,  57,  59,  60,  166 

restiforme  (ia) 102,  IIH,  132,  144,  150 

striatum  (a) 7,  25,  35,  55,  56,  76,  84,  210 

Cortex  near  calcarine  fissure 74 

VIII 


INDEX. 


Cortex  near  Sylvian  fissure "iS 

Cortical  fillet 80,    90 

Cortical  gray  matter  of  cerebellum 111-113 

Cortical  gray  matter  of  cerebrum 70-76 

Cranial  reflexes 199 

Cranial  and  spinal  reflexes 200,  201 

Crossed  descending  tract  from  red  nucleus 65,  88,  125,  142,  176 

Crossed  paralysis 127,  149 

Crossed  pyramidal  tract 130,  143,  147 

Crossing  of  main  sensory  path 170 

Crura  ad  cerebrum 102 

Crura  ad  meduUam 102 

Crura  ad  pontem 103 

Crus  cerebri 7 

Crus  fornicis 32 

Crusta  (se) 7,  53-56,  66,  85-89,  215 

Culmen  monticuli  cerebelli 106 

Culmen  and  anterior  crescentic  lobules 106 

Cuneate  lobe 17,    90 

Cuneate  nucleus .'.   132 

Cuneate  tubercle 133,  147 

Cuneus 17 


Declive  monticuli  cerebelli 106 

Decussatio  lemniscorum 136 

Decussation  of  pyramids 129,  130 

Deep  nuclear,  or  rust-colored  granular  layer  of  cerebellum.  .112,  113 

Deep  origin  of  anterior  root  of  spinal  nerves 180 

Deep  origin  of  posterior  root  of  spinal  nerves 181,  182 

Defecation  center 168 

Defecation  reflex 198,  199 

Degeneration  of  Nissl 68 

Degeneration  of  Waller 68 

Dendrites - 66 

Dentate  fascia.. 40,  41 

Derivatives  of  brain  vesicles 207,  208 

Descending  tracts  of  cord 172,  173 

IX 


INDEX. 

PAGE. 

Descending  root  of  trifacial  nerve 88,  125 

Development  of  brain 205-219 

Development  of  cerebrum 208-214 

Development  of  olfactory  lobe 208 

Development  of  interbrain 213,  214 

Development  of  midbrain 214,  215 

Development  of  cerebellum 215,  216 

Development  of  pons  varolii 216 

Development  of  medulla  oblongata 217-219 

Development  of  spinal  cord 220-224 

Diaphragm  sellas .' 2 

Diencephalon 7,  42,  205 

Digitationes  hippocampi 41 

Digastric  lobules  of  cerebellum 110 

Direct  cerebellar  tract  116,  132,  142,  144,  169,  175 

Direct  pyramidal  tract 130,  138,  174 

Dorsal  surface  of  pons 120 

Dorsal  transverse  fibers  of  pons 121 

Dorsal  aeep  transverse  fibers  of  pons 121 

Dorsal  deep  longitudinal  fibers  of  pons 123 

Dorsal  longitudinal  fibers  of  pons 125 

Dorsal  nucleus  of  auditory  nerve 153 

Dorsal  surface  of  medulla , 132 

Dorsal  zone  of  embryo 205,  214,  215,  217,  219,  220 

Dorso-lateral  groove  of  medulla 129 

Dorso-ventral  fibers  of  medulla 136,  137 

Dorso-lateral  cerebellar  tract 175 

Dorso-ventral  fibers  of  spinal  cord 172 

Dura  mater  encephali 1 

Dura  mater  of  spinal  cord 159,  160 

Dura  mater  spinalis 159,  160 

E 

Edinger's  bundle 77,    84 

EJBEerent  or  motor  paths *. 185-190 

Eighth  cranial  nerve 144 

Ejaculation  center 168 

Eleventh  nerve 131 

X 


INDEX. 

PAGE. 

Embryology  of  brain  and  spinal  cord 202-224 

Eminentia  acustici 153 

Eminentia  cinerea 152 

Eminentia  collateralis 40 

Eminentia  medialis 152 

Eminentia  teres 145,  151,  152 

End-brush 67 

End-arteries  of  Cohnheim 97 

End -organs 66 

Enlargements  of  spinal  cord 163 

Epencephalon  .....' 205,  215,  216 

Ependyma 34 

Epiphysis  cerebri  (see  pineal  body) 

Epithalamus 78 

Erection  center 168 

Exceptions  to  typical  cortex 74 

Exterior  surface  of  cerebrum 9 

External  accessory  olivary  nucleus 148* 

External  arciform  fibers 116,  132,  135,  144,  147 

External  capsule 25 

External  geniculate  bodies 7,  49,  50,  60,  76,  82,    90 

External  nucleus  of  optic  thalamus  (or  lateral) 78 

Extremities  of  optic  thalamus 49 

F 

Facial  nerve 135 

Facial  paralysis 127,  189 

Facies  anterior  (medullas) 130 

Facies  basalis  cerebri 17 

Facies  cerebelli  inferior 107 

Facies  cerebelli  superior 103  - 

Facies  convexa 9 

Facies  lateralis 131 

Facies  medialis 14 

Facies  posterior  (medulla) *.  .^ .- 134 

Falx  cerebelli 1 

Falx  cerebri 1 

Fascia  dentata  hippocampi 41 

XI 


INDEX. 

PAGE. 

Fasciculus  antero   ateralis  superficialis  (ascendens,  descendcns) 

131,  141,  174 

Fasciculus  cerebello-spinalis 144,  175 

Fasciculus  cerebro-spinalis  anterior  (ventralis) 138,  174,  176 

Fasciculus  cerebro-spinalis  lateralis 138,  176 

Fasciculus  cuneatus 132,  142,  143,  150,  1 77,  219 

Fasciculus  gracilis 132,  142,  143,  150,  179,  219 

Fasciculus  longitudinalis  (inferior) 93 

Fasciculus  longitudinalis  (medialis) 61,  124,  139,  173 

Fasciculus  longitudinalis  (superior) 93 

Fasciculus  longitudinalis  pyramidalis  pontis 55,  86,  122 

Fasciculus  longitudinalis  ventralis 140 

Fasciculus  marginalis 177 

Fasciculus  occipito-frontalis 93 

Fasciculus  perpendicularis 94 

Fasciculus  proprius  antero-lateralis 131, 141,  173 

Fasciculus   retroflexus 79,    84 

fasciculus  Rolandi 132,  142,  143.  219 

Fasciculus  solitarius 145,  218 

Fasciculus  tegmenti  centralis 64,  124 

Fasciculus  teres 145,  218 

Fasciculus  thalamo-mamillaris 20,  33,    79 

Fasciculus  triangularis  (Hel wigi) 64 

Fasciculus  uncinatus 93 

Fasciculus  ventralis 124,  174 

Fastigium  (ventriculi  quarti) 114,  151. 

Fibers  of  internal  capsule 85-90 

Fibers  of  tegmentum 60-65,    89 

Fibrae  arcuatae  external  anterior,  posterior 131,  135 

Fibrae  cerebello-olivares 136,  148 

Fibrae  pontis  superficiales 121 

Fifth  temporal,  infracalcarine  or  lingual  convolution 17 

Fifth  ventricle 33,  212 

Fillet 50,  62,  123.  124 

Fillet  decussation 136,  219 

Fillet  of  gyrus  fornicatus 92 

Filum  terminale 161,  163 

First  temporal  convolution 14 


INDEX. 

PAGE. 

First  temporal  sulcus 13 

Fissura  calcarina 45 

Fissura  choroidea 9,     16 

Fissura  collateralis 16 

Fissura  hippocampi 15 

Fissura  lateralis  cerebri   ....    10 

Fissura  longitudinalis  cerebri 9 

Fissura  mediana  anterior,  posterior 128,  132,  163,  164 

Fissura  prima 22,  24,    30 

Fissura  transversa  cerebri 9 

Fissurae  interlobulares 10,  104 

Fissurae  orbitales 22 

Fissural  ventricle  (see  fifth  ventricle). 

Fissural  veins , , 183 

Fissure  of  Rolando 10 

Fissure  of  Sylvius 10 

Fissures  of  convex  surface  of  cerebrum 9-11 

Fissures  of  inferior  surface  of  cerebrum 51 

P'issures  of  lower  surface  of  cerebellum .107,  108 

Fissures  of  medial  and  tentorial  surface 14-16 

Fissures  of  spinal  cord 163-165,  223,  224 

Fissures  of  superior  surface  of  cerebellum 104,  105 

Fissures  or  sulci 9 

Flexures  of  nural  tube , 206 

Flocculi  (cerebelli) 109,  151 

Floor  of  fourth  ventricle 151 

Folium  cacuminis  and  posterior  lobules  of  cerebellum 106 

Folium  vermis 107 

Foramen  caecum  of  Vicq  d'Azyr 130 

Foramen  interventriculare  (Monroi) 34,    43 

Foramen  of  Magendie 5,  133,  150 

Foramen  of  Monro 32,  34,  42,  43,  44,  208,  211 

Foramen  of  Key  and  Retzins 5,  133,  150 

Forceps  major 39 

Formatio  reticularis  alba 138,  139 

Formatio  reticularis  grisea 140 

Formatio  reticularis  of  medulla 134 

Fornix 7,  31,  32,  35,  92,  210.  211 

XIII 


INDEX. 

PAGE. 

Fossa  interpeduncularis 53 

Fossa  rhomboidea  inferior 163 

Fourth  cranial  nerve 53,  120 

Fourth  temporal,  or  fusiform,  convolution 17 

Fourth  ventricle 100,  129.  150-158,  217 

Fovea  inferior 152,  153,  218 

Fovea  superior 151,  218 

Fraenula  (cerebelli) 105 

Frontal  lobe 11 

Fronto  parietal  operculum ; 10,  12,  22 

Fronto-pontal  tract 27,  86 

Function  of  cerebellum 100 

Function  of  fillet 62 

Functions  of  neurones 68 

Functions  of  stellate,  basket  and  granule  cells 113 

Funiculus  anterior  and  f.  lateralis. 167 

Funiculus  antero-lateralis 173 

Funiculus  lateralis 131,  169 

Funicilus  posterior 169,  177 

Fusiform  cell  bodies  of  cortex 74 

functions  of 74 

Fusions  of  hemispheres  with  each  other. 211 

Fusions  of  hemispheres  with  thalamencephalon 211 


Ganglion  interpedunculare '. 57 

Ganglion  spinale 181 

Ganglionar  gray  matter  of  cerebellum 113 

Ganglionar  gray  matter  of  cerebrum  and  midbrain 70-85 

Ganglionic  system  of  arteries 96,    97 

General  cavity  of  cerebrum 30 

General  sensory  paths 190-193 

Genital  centers 168 

Genu  and  truncus  of  corpus  callosum 30,  31,    39 

Genu  of  facial  nerve 61,  140,  146 

Genu  of  internal  capsule 27,    86 

Germinating  cells  (His) 204 

XIV 


INDEX. 

PAGE 

Globus  pallidas 36,64 

Glossopharyngeal  nerve 137,  156 

GoU's  column 143,  179 

Gower's  column 175 

Gracile  nucleus 132 

Grand  divisions  of  brain 6,       7 

Granulationes  arachnoideales 3 

Gray  and  white  matter  of  cerebrum  and  midbrain 66-99 

Gray  commissure  of  cord 168 

Gray  crescent  of  cord 165-171 

Gray  matter  of  brain  and  cord 68 

Gray  matter  of  cerebellum 103 

Gray  matter  of  cerebrum  and  midbrain 70-85 

Gray  matter  of  cord 165-171 

Gray  matter  of  formatio  reticularis  pontis % . .  126 

Gray  matter  of  medulla 146,  149 

Gray  matter  of  pons 126,  127 

Great  longitudinal  fissure 8,      9 

Great  transverse  fissure 5, 31,  40,    49 

Gudden's  commissure 20,    51 

Gustatory  conduction  paths 197 

Gyri  insulae-Gyri  breves-Gyrus  longus 14 

Gyri  occipitales  laterales 13 

Gyri  operti 14 

Gyri  orbitales 22 

Gyrus  angularis 12 

Gyrus  centralis,  anterior,  posterior 11,    12 

Gyrus  cinguli . 16 

Gyrus  fornicatus 16 

Gyrus  frontalis,  superior,  medius,  inferior 11 

Gyrus  f usiformis 17 

Gyrus  hippocampi 16 

Gyrus  lingualis 17 

Gyrus  rectus 22 

Gyrus  supramarginalis 12 

Gyrus  temporalis  superior,  medius,  inferior 14 


XV 


INDEX. 

PAGE. 

Habenula 45 

Hatteria 46 

Helwig's  triangular  tract 124,  141,  148,  175 

Hemispheres  of  cerebellum 100 

Hemispheres  of  cerebrum 7,     8 

Hemisphere  vesicle 208 

Hemispherium  cerebelli 100 

Hemispherium  cerebri 7,      8 

Hind-brain 7,  100-127 

Hippocampal  convolution ; 16 

Hippocampal  fissure 15 

Hippocampus 40 

Hippocampus  major 40,    75 

Hippocampus  minor 39 

Histologic  layers  of  embryo 205,  218,  219,  221,  222 

Histologic  layers  of  spinal  cord 221,  222 

H-shaped  column  of  gray  matter  in  medulla 146,  166 

Hylus  nuclei  dentati    . .  113 

Hypophysis  cerebri 19 

Hypoglossal  nerve 129,  131,  137,  156 

Hypoglossal  trigone 145,  152 

Hypothalamic  body 50 

Hypothalamic  nuclei 48 

Hypothalamic  tegmental  region 50,    53 

Hypothalamus 50 

I 

Indirect  motor  paths 55,  56,  86 

Inferior  cerebellar  veins 1 18 

Inferior  cerebral  veins : 98,    99 

Inferior  fovea 152,  153,  218 

Inferior  frontal  convolution 11 

Inferior  frontal  sulcus 11 

Inferior  gray  commissure  of  cerebrum 19 

Inferior  lamina  of  internal  capsule 26,    40 

Inferior  lamina  of  medullary  stem 101,  114 

Inferior  longitudinal  fasciculus 93 

XVI 


INDEX. 

PAGB. 

nferior  longitudinal  sinus 2,    47 

nferior  medullary  vellum 101,  133,  150 

nferior  occipital  convolution  or  gyrus 13 

nferior  occipital  sulcus 13 

nferior  olivary  nucleus 148 

nferior  olive 64 

nferior  parietal  convolution 12 

nferior  peduncles  of  cerebellum  (restiform  body).  ..102,  116,  150,  216 

nferior  rhomboid  fossa 163 

nferior  sensory  root  of  trifacial  or  fifth  nerve 125,  143,  145 

nferior  surface  of  cerebellum 107,  111 

nferior  surface  of  cerebrum 24-51 

nferior  surface  of  pons 119 

nfundibulum 7,  18,  19,  214 

nner  or  ependymal  layer  of  medulla 218 

nsula 14 

nterbrain 7,  42-51,    66 

nterior  of  medulla 133,  149 

nterior  of  midbrain 54,    65 

ntermediate  bundle  of  crusta 55,  77,  85,  86,  187 

ntermedio-lateral  column  of  cells 168 

nternal  accessory  vlivary  nucleus 148 

nternal  arciform  fibers 135,  116 

nternal  capsule 26-28,  31,  35,  36,  40,  53,  54,  55,  211 

nternal  geniculate  bodies 7,  49,  50,  51,  51,  57,  60,  76,  82,  215 

nternal  nucleus  of  optic  thalamus  (or  medial) 78 

nternal  orbital  convolution 22 

nterolivary  fillet 62,  139,  147,  178 

nterpeduncular  ganglion 57,    79 

nterpeduncular  structures 18,    48 

ntraparietal  fissure 12 

ntumescentia   cervicalis 163 

ntumescentia  lumbalis 163 

sland  of  Reil 10-14,    22 

sthmus 16,    52 

sthmus  gyri  fornicati 16 

sthmus  rhombencephali 52 

ter  a,  tertia  ad  quartum  ventriculum , 58 

XVII 


INDEX. 

PAGE. 

Jugular  vein — internal 3 

L 

Lamina  cinerea 7, 18,  31,  44,  47,  84,  214 

Lamina  perforata  anterior 24 

Lamina  terminalis 19,  31, 43,    48 

Laminae  medullares  (cerebelli) 114 

Large  pyramids  of  cerebral  cortex 73  " 

function  of 73 

Lateral  area  of  medulla 140 

Lateral  cerebellar  veins 120 

Lateral  extremity  of  corpus  callosum 30 

Lateral  fillet  (or  lower) 60,  63,  83,  120,  122,  139 

Lateral  horn  (of  cord) 166 

Lateral  nucleus  of  medulla  140 

Lateral  recesses  of  fourth  ventricle 114, 133,  151 

Lateral  sinus 2 

Lateral  surface  of  medulla 131,  132 

Lateral  sulcus  of  midbrain 54 

Lateral  tract  of  medulla 131 

Lateral  ventricles 31,  33,  34-42 

Lateral  white  column  of  cord 167,  169 

Lemniscus 50,  123,  124 

Lemniscus  interolivaris  (L.  medialis,  L.  superior) 62,  139 

Lemniscus  lateralis 60,  62,  63,  120,  123,  139 

Lemniscus  medialis 56,  62,  63,  120,  123,  139 

Lemniscus  superior 62,  123,  139 

Lenticular  nucleus 25,  26,  36,    37 

Lesions  of  acustic  radiations 9 

Lesions  of  anterior  corner 167 

Lesions  of  anterior  quadrigeminal  bodies 83 

Lesions  of  association  centers 72 

Lesions  of  corpus  striatum 77 

Lesions  of  cortical  fillet 90 

Lesions  of  lower  motor  neurones 180 

Lesions  of  medulla 149 

Lesions  of  motor  and  sensory  cortex. ; 72 

Lesions  of  motor  tracts  (upper) 89 

XVIII 


INDEX. 

PAGB. 

Lesions  of  olfactory  tract,  or  cortex 75 

Lesions  of  pons 127 

Lesions  of  posterior  column  of  cord 179 

Lesions  of  posterior  quadrigeminal  bodies 83 

Lesions  of  posterior  roots  of  spinal  nerves 182 

Lesions  of  pyramidal  tract 177 

Lesions  of  sensory  paths 193 

Lesions  of  special  sense  paths 193 

Lesions  of  trochlear  and  oculomotor  nuclei 84 

Ligamentum  denticulatum 160 

Ligula 133 

Limbic  lobe 16,    17 

Lingula  and  traenula  of  cerebellum 105 

Lissauer's  tract 177 

Lobes  of  cerebellum,  inferior  surface 108-111 

Lobes  of  cerebellum,  superior  surface 105-107 

Lobes  and  convolutions  of  cerebrum,  convex  surface 11-14 

Lobes  and  convolutions  of  cerebrum,  inferior  surface 21,    24 

Lobes  and  convolutions  of  cerebrum,  medial  and  tentorial  sur- 
face   16.     17 

Lobulus  biventer  110 

Lobulus  paracentralis 11,    17 

Lobulus  parietalis  superior,  inferior 12 

Lobulus  semilunaris  inferior 107 

Lobulus  semilunaris  superior 110 

Lobus  cacuminis 106 

Lobus  centralis  (cerebelli) 105 

Lobus  cli vi 106 

Lobus  culminis 106 

Lobus  frontalis 11 

Lobus  lingulae 105 

Lobus  noduli 109 

Lobus  occipitalis 13 

Lobus  olfactorius 23 

Lobus  orbitalis 21 

Lobus  parietalis 12 

Lobus  pyramidalis 110 

Lobus  quadrangularis * 106 

XIX 


INDEX. 

PAGE 

Lobus  temporalis 18 

Lobus  tuberis 1 10 

Lobus  uvulae 109 

Location  of  Rolandic  fissure 10 

Location  of  Sylvian  fissure 10 

Locomotor  ataxia 179,  182 

Locus  coeruleus 151,  152 

Loevventhal's  column 174 

Long  association  fibers  of  cerebrum 92 

Long  sensory  tract  (Ciagliniski) 171 

Longitudinal  fibers  of  cord 172,  179,  222 

Longitudinal  fibers  of  medulla 137-146 

Longitudinal  fibers  of  pons 122,  125 

Longitudinal  sinus,  inferior 2 

Longitudinal  sinus,  superior 2 

Longitudinal  striae,  lateral 30 

Longitudinal  striae,  medial   29 

Longitudinal  tract  of  cord 172-179.  222,  223 

Lower,  or  closed,  medulla r 142 

Lumbar  enlargement  of  cord 163 

Lymph  spaces  of  cerebellum 118 

Lymph  spaces  of  cerebrum 99 

Lymph  spaces  of  spinal  cord 184 

Lyre 32,    91 

M 

Mantle  (or  middle)  layer  of  embryo 205 

Mantle  layer  of  medulla 218,  219 

Mantle  layer  of  spinal  cord 221,  222 

Marginal  convolution 17 

Marginal  tract  of  Lissauer 177 

Massa  intermedia 43,  48,    84 

Medial  cerebral  veins 98 

Medial  fillet 56,63,83,  139 

Median  sulcus  of  midbrain 53,    54 

Medulla  oblongata 7,  128-149 

Medulla  spinalis 168 

Medullary  stem  of  cerebellum 101-103,  114-  116 

XX 


tNt)EX. 

PAGtJ. 

Medulli-spinal  veins 160,  161,  183 

Membranes  of  brain 1-6 

Membranes  of  spinal  cord 159-161 

Meninges  encephali 1 

Meninges  of  brain 1-6 

Meninges  of  cord 159-161 

Meningo-rachidian 4,  159,  184 

Mesencephalon 7,  52,  205,  214,  215 

Metathalamus 49 

Metencephalon 7,  129,  205,  217-219 

Methods  of  locating  tracts  of  cord 172 

Meynert's  commissure 81,    84 

Midbrain 7,  52-99 

Middle  association  center 72 

Middle  cerebral  artery 95 

Middle  cerebral  vein 99 

Middle  commissure  of  cerebrum 7,  48,    84 

Middle  frontal  convolution 11 

Middle  horn  of  lateral  ventricle  (descending) 39 

Middle  longitudinal  fibers  of  pons 123-125 

Middle  occipital  convolution  or  gyrus 13 

Middle  occipital  sulcus 

Middle  peduncle  of  cerebellum 103,  115,  216 

Middle  transverse  fibers  of  pons 121 

Micturition  center 168 

Mitral  neurones 74 

Mixed  tracts  of  cords,,  ascending  and  descending .    . ... .  .172,  173 

Motor  areas  of  cerebral  cortex 12,  71,  72 

Motor  centers  of  medial  surface  of  cerebrum 17 

Motor  fibers  of  internal  capsule 27,  85-89 

Motor  fibers  to  arm 55,  87 

Motor  fibers  to  head 55,  56,  87 

Motor  fibers  to  leg  and  foot 56,  88 

Motor  fibers  to  trunk 56,  88 

Motor  head  area 70 

Motor  lower  extremity  area 70 

Motor  memories 71 

Motor  nuclei  of  cranial  nerves 55,  56,  87,  156,  157 

XXI 


INDEX. 

PAGE. 

Motor  ocufi  or  third  cranial  nerve 20, 53,  58,  51),  140 

Motor  or  efferent  paths 185-190 

Motor  projection  fibers  of  cerebrum 85-89 

Motor  projection  fibers  to  cranial  nerves 87 

Motor  speech  center 12,  70,  93 

Motor  trunk  area .^ 70 

Motor  upper  extremity  area 70 

Motor  writing  center 70 

Myelencephalon 7,  205 

Myelospongium 205 


Naming  center 71 

Nerve  supply  of  membranes  of  cord 161 

Nerves  of  dura  mater 4 

Nerves  of  Lancisi 17,  29,  30 

Nerves  of  pia 6 

Nervi  oltactorii 23,  154 

Nervus  opticus 21,  154 

Nervus  abducens 155 

Nervus  accessorius 156 

Nervus  acusticus 144,  155 

Nervus  cochlearis 120 

Nervus  facialis 155 

Nervus  glassopharyngeus 156 

Nervus  hypoglossus 137,  156 

Nervus  intermedius 155 

Nervus  oculomotorius 20,  154 

Nervus  trigeminus 120, 155 

Nervus  trochlearis 20,  59,  154 

Nervus  vagus 156 

Neural  crest 202-204 

Neural  tube 204-224 

Neuraxones  (or  axones) 67 

Neuroblasts 204 

Neuroglia 67,  205 

Neurogliar  layer  of  medulla 219 

Neuron 68 


INDEX 

PAGE. 

Neurone 66 

Neurone  center  (cell  body ) 65 

Neurones  of  cajal 72 

Ninth  nerve 131 

Nodulus  and  flocculi 109 

Nodulus  vermis 109 

Note  on  the  neurone 68 

Nuclei  of  cranial  nerves  (ventral  series) 156 

Nuclei  of  cranial  nerves  (dorsal  series) 156 

Nuclei  of  optic  thalamus 78 

Nuclei  of  pons 55,  56, 122,  126,  216 

Nuclei  of  Stilling 113 

Nuclei  of  Stilling  (in  cord) '. 169 

Nucleus  accessorius  dorsalis 148 

Nucleus  accessorius  medialis 148 

Nucleus  ambignus 140,  146 

Nucleus  amygdalae 37 

Nucleus  arcuatus 149 

Nucleus  candatus  (see  candate  nucleus) 37 

Nucleus  cuneatus 62,  136,  143,  147,  219 

Nucleus  dentatus 113 

Nucleus  dorsalis 168 

Nucleus  emboliformis 113 

Nucleus  fastigii 114 

Nucleus  globosus 113 

Nucleus  gracilis 62,  136, 143,  147,  219 

Nucleus  hypothalamicus 50,  57,  81 

Nucleus  lentiformis 36 

Nucleus  magno-cellularis 127 

Nucleus  of  abducent,  or  sixth  cranial  nerve .145,  152,  216,  219 

Nucleus  of  external  arciform  fibers 149 

Nucleus  ot  facial,  or  seventh  cranial  nerve 216 

Nucleus  of  fifth  nerve  (inferior) 147 

Nucleus  of  formatio  reticularis 126 

Nucleus  of  glossopharyngeal,  or  ninth  nerve.. 153 

Nucleus  of  habenula 78 

Nucleus  of  lateral  fillet 63,  122 

Nucleus  of  Luys  (Luysi) 50,  57,  76,  81,  84 

XXIII 


INDEX. 

PAGE. 

Nucleus  of  ninth,  tenth  and  eleventh  cranial  nerves 146, 147,  219 

Nucleus  of  pneumogastric,  or  tenth  nerve 153 

Nucleus  of  pons  (see  nucleus  pontis) 55,    56 

Nucleus  of  pulvinar 78 

Nucleus  of  Rolando 143,  219 

Nucleus  of  superior  olive '. . 63,  122,  126,  216 

Nucleus  of  third  and  fourth  nerves 58, 59,  84,  215 

Nucleus  of  trapezium 121.  122,  126 

Nucleus  of  trapezoid  body 63 

Nucleus  of  trifacial,  or  fifth  nerve  (motor) 152,  216 

Nucleus  of  twelfth,  or  hypoglossal,  cranial  nerve 146,  219 

Nucleus  olivaris  (medullae) 148 

Nucleus  olivaris  superior 126 

Nucleus  pontis 55,56,  122,126,  216 

Nucleus  ruber 50,  57,    81 

O 

Obex 133 

Occipital  lobe 13 

Occipital  sinus 2 

Oculomotor  groove 53 

Oculomotor  nerve 154 

Oculomotor  nucleus 58 

Olfactory  bulb 22,  74 

Olfactory  conduction  paths 75,  194 

Olfactory   lobes 7,  22,  208 

Olfactory  nerve 154 

Olfactory  tract 22,  23 

Olfactory  trigone 22,  24 

Olivary  body  (of  medulla) 131,  219 

Olivary  bundle  of  spinal  cord 148 

Olivary  fasciculus 64,  77,124,  141 

Olivary  nucleus  external  accessory 140 

Olivary  nucleus  internal  accessory 140 

Olivary  nucleus  of  medulla 140,  148 

Olivary  peduncle 136 

Operculum 10,  12 

orbital 10 

XXTV 


INDEX. 

PAGE. 

frontal 10 

f  ronto-parietal 10,     12 

Optic  chiasm  or  commissure 18,    20 

Optic  conduction  path 194,  195 

Optic  lobes 82 

Optic  nerve 154 

Optic  radiations 80 

Optic  recess 48 

Optic  thalamus  (i) 7,  26,  31,  35,  37, 44, 48,  76,  78-81,  214 

Optic  tracts  and  commissure 7,  18,    44 

Optic  vesicle 213 

Orbital   lobe 21 

Orders  of  neurones 68 

Origin  of  cranial  and  spinal  ganglia 202,  203 

Origin  of  cranial  nerves 153-158 

Origin  of  medulla 129 

Origin  of  meninges 202 

Origin  of  neurones 204 

Origin  of  optic  nerves,  chiasm  and  tracts 213 

Origin  of  spinal  cord 162 

P 

Pacchionian  bodies 3 

Paracentral  lobule 11,    17 

Parietal  lobe 12 

Parieto-occipital  fissure 11,     15 

Pars  anterior  commissurae  anterioris 47 

Pars  anterior  lobuli  quadrangularis 106 

Pars  basilaris  pontis 119,  121 

Pars  dorsalis-pontis 119,  121,  122 

Pars  frontalis  capsulae  internae 27 

Pars  intermedia 155 

Pars  occipitalis  capsulae  internae , 27 

Pars  posterior  commissurae  anterioris 47 

Pars  posterior  lobuli  quadrangularis 106 

Parturition  center 168 

Pedes  pedunculi  (see  crustae) 7 

Peduncle  of  flosculus. 109 

XXV 


INDEX. 

PAGE. 

Pedunculus  cerebri   (see  midbrain) 7 

Pedunculus  flocculi 109 

Perikaryon  (or  neurone  center) 66,  167,  168 

Permanent  fissures  of  cerebrum 209,  210 

Perpendicular  fasciculus 94 

Pes  hippocampi 40,    41 

Petrosal  sinuses,  inferior  and  superior 3,  99,  118 

Pia  mater  encephali 5 

Pia  mater  of  brain 5 

Pia  mater  of  spinal  cord 160 

Pia  mater  spinalis 5,  160 

Pillars  of  fornix '. 20,  32,  210,  211 

Pineal  body 7,  31,  43,  45,  214 

Pineal  stalk 45 

Pineal  striae 46 

Pituitary  body 18,     19 

Plexus  choroideus  ventriculi  quarti 38,  133,  153 

Plexus  choroideus  ventriculi  tertii 45,    47 

Plexus  venosi  vertebrales  interni 159,  184 

Pneumogastric  or  vagus  nerve 130, 131,  156,  157 

Pneumogastric  trigone 153 

Points  of  difference  between  dura  of  brain  and  cord 4 

Polymonphous  layer  of  cortex 73 

function  of 73 

Pons  varolii 7,  118-127 

Ponticulus  of  Arnold ." 130 

Postcentral  convolution  or  gyrus 11 

Postcentral  fissure  (of  cerebellum)  104 

Postcentral  fissure  or  sulcus 12 

Postclival"  fissure 104 

Postnodular  fissure 107 

Postparietal  convolution 12 

Postpyramidal  fissure 108 

Posterior  association  center 71 

Posterior  area  of  medulla 142-146 

Posterior  brachium 51,83,90,  215 

Posterior  cerebellar  notch 101 

Posterior  cerebral  arteries 95,    96 

xxyi 


INDEX. 

PAGE 

Posterior  choroid  tela  ( or  inferior) 6,  133 

Posterior  communicating  arteries 95 

Posterior  commissure  of  cerebrum 7,  31,  42,  43,  44,  53,  214 

Posterior  commissure  of  cord 165,  169 

Posterior  cornu  in  medulla 147 

Posterior  cornu  of  cord 166,  169,  171 

Posterior  cornu  (or  horn)  of  lateral  ventricle 39 

Posterior  crescentic  lobules  of  cerebellum 106 

Posterior  fenestrated  septum 160 

Posterior  inferior  cerebellar  artery 117 

Posterior  intermediate  furrow 165 

Posterior  longitudinal  bundle 50,  61,  124, 139, 140,  173,  174 

Posterior  median  fissure  of  medulla. 128 

Posterior  median  fissure  of  cord 164,  223 

Posterior  nucleus  of  optic  thalami 78 

Posterior  olfactory  lobule 22,    24 

Posterior  orbital  .convolution 22 

Posterior  perforated  lamina  ( or  space) 31,  44,    53 

Posterior  quadrigeminal  body 63,  76    83 

Posterior  root  of  spinal  nerves 180,  182 

Posterior  sclerosis 179 

Posterior  segment  of  internal  capsule 27 

Posterior  spinal  artery 161,  182,  183 

Posterior  white  column  of  cord 169 

Postero-inferior  lobules  of  cerebellum 110 

Postero-lateral  choroid  artery 38,    97 

Postero-lateral  fissure  of  cord 164,  223 

Postero-lateral  ganglionic  arteries 97 

Postero-lateral  tract  of  cord 177,  178 

Postero-medial  choroid  artery 98 

Postero-medial  tract  of  cord 179 

Postero-median  ganglionic  arteries 97 

Postero-superior  lobules  of  cerebellum 106 

Precentral  convolution  11 

Precentral  fissure,  or  sulcus,  of  cerebellum 104 

Precentral  fissure,  or  sulcus,  of  cerebrum 11 

Preclival   fissure 104 

Prepyramidal  fissure 108 

XXVII 


INDEX. 

PAG?!. 

Primary  brain  vesicles 204 

Primary  sulci  of  cerebrum 209 

Processus  reticularis 166 

Projection  or  peduncular  fibers  of  cerebellum. , 114-116 

Projection  or  peduncular  fibers  of  cerebrum 85-91 

Prosencephalon 7,  9,  205,  207,  208-213 

Pulvinar  of  optic  thalamus 40,  41,  49,  90 

Pupillary  reflex 200 

Pupillp-dilator  tract 124,  140 

Putamen 36 

Pyramid  and  digastric  lobules 110 

Pyramid  of  medulla 130,  138 

Pyramidal  conduction  paths 185,  186 

Pyramidal  tract 27,  55,  86,  89,  122 

Pyramis  medullae  oblongatae 138 

Pyramis  vermis .' 110 

Q 

Quadrate  lobe 17 

Quadrigeminal  bodies 57,  82,  83 

Quadrigeminal   lamina 60 

Qualities  pecular  to  axones 68 

Qualities  peculiar  to  dendrites 68 

R 

Radiatio,  occipito-thalamica  (Gratioleti) 28,  80 

Radiatio  temporo-thalamica. 28,  81 

Radix  anterior  (nervi  spinalis) 180 

Radix  cerebralis  nervi  accessorii 137 

Radix  medialis  lateralis  (nervi  optici) 21 

Radix  nervi  glossopharyngei 137 

Radix  nervi  vagi 137 

Radix  nervi  vestibularis 137 

Radix  posterior  (nervi  spinalis) 180 

Radix  spinalis  nervi  trigemini 145 

Raphe  (of  medulla) 135 

Real  central  terminations  of  posterior  spinal  roots 181 

Recessus  lateralis  ventriculi  quarti 114 

XXVIII 


INDEX. 

PAGJI. 

Red  nucleus 50,  57,  64,  81 

Reflex  centers  of  cord 168 

Reflex  paths 198,  201 

Region  of  speech 12,    70 

Respiratory  reflex , 200 

Restiform  body 132, 'l33,  143,  144,  219 

Reticula  of  cord 166 

Rhinencephalon 17,  93 

Rolandic  nucleus 132 

Roof  epithelium  of  fourth  ventricle 133,  151 

Roof  epithelium  of  third  ventricle 31,  43,  44 

Roots  of  auditory  nerve 144 

Roots  of  olfactory  tract 23 

Roots  of  optic  tract 21,  51 

Roots  of  spinal  nerves 179,  182 

Root  veins 183 

Rostrum  of  corpus  callosum 30,  39 

S 

Second  temporal  convolution  or  gyrus 14 

Second  temporal  fissure  or  sulcus 13 

Secondary  brain  vesicles 205 

Secretory  centers 168 

Sensory  areas  of  cerebrum 70 

Sensory  conduction  paths 190-197 

Sensory  decussation     62,  136,  147,  219 

Sensory  fibers  of  internal  capsule 27.  89-91 

Septomarginal  tract 118,  170 

Septum  lucidum 31,  33,  35,39  211 

Septum  pellucidum T 33 

Septum  subarachnoideale 160 

Seventh  cranial  nerve  (facial) 124 

Short  association  fibers  of  cerebrum ' 91 

Sinus  basilaris , 3 

Sinus  cavernosus 3 

Sinus  circularis 3 

Sinus  occipitalis 2 

Sinus  petrosus  superior  et  inferior 3 

XXIX 


INDEX. 

PAGE. 

Sinus  rectus 2 

Sinus  sagittalis  superior  and  inferior 2,  98,    99 

Sinuses  of  dura  mater 2,    3 

Sixth  cranial  nerve  (abducent) 61,  124 

Sixth  ventricle 162 

Small  pyramids  of  cerebral  vortex 72 

functions  of 73 

Solitary  bundle 145,  218 

Somaesthetic  area 13,  26,  28,    70 

Special-sense  conduction  paths 194-197 

Spinal  accessory  nerve 156 

Spinal  and  cranial  reflexes 199,  200 

Spinal  bulb 128 

Spinal  cord 162-184,  220-224 

Spinal  cord  in  foetus 162 

Spinal  ganglion 181,  203 

Spinal  reflexes 198,  199 

Spinal  root  of  trifacial  (or  fifth)  nerve 143 

Splenium  of  corpus  callosum 29,    31 

Spongioblasts 205 

Stellate  cells  of  cerebellum Ill 

Strabismus 127 

Straight  sinus.. 2 

Stratum  cmereum 82 

Stratum  dorsale  hypothalami 50,    64 

Stratum  glomerulosum 74 

Stratum  lemnisci 82 

Stratum  opticum 82 

Stratum  zonale 49,    82 

Stria  medullaris  thalami - 46 

Stria  terminalis 37 

Striae  longitudinales  laterales  et  mediates 29,    30 

Striae  medullares 151 

Striae  olfactorii  lateralis,  medialis,  intermedia 23 

Subarachnoid  spaces 5,  160,  161 

Subarachnoid  tissue. . .    4 

Substance  of  spinal  cord 160-182 

Substantia  alba  (of  cord) 171-182 

XXX 


INDEX. 


Substantia  cinerea  gelatinosa  Rolandi 166 

Substantia  gelatinosa  Rolandi 166 

Substantia  grisea 165 

Substantia  intermedia  grisea 166,  168 

Substantia  nigra 7,  50,  54,  56,  57,  66,  76,  83 

Substantia  perforata  posterior 53,  57 

Substantia  spongiosa 166 

Sulcus  ( i)  centralis 10 

Sulcus  centralis  insulae 14 

Sulcus  cinguli 15 

Sulcus  circularis  (Reili) 14,  22 

Sulcus  frontalis  superior  et  inferior 11 

Sulcus  horizontalis  cerebelli 101 

Sulcus  interparietalis 12 

Sulcus  intermedius  posterior  (of  cord) ' 165 

Sulcus  (i)  lateralis  (mesencephali) 53 

Sulcus  lateralis  anterior  (medullae) 129 

Sulcus  lateralis  posterior  (medullae) 130 

Sulcus  lateralis  posterior  (of  cord) 165 

Sulcus  limitans  insulae 14,  22 

Sulcus  longitudinalis  fossae  rhomboideae 151 

Sulcus  mediana  anterior  (of  cord) 163 

Sulcus  mediana  posterior  (of  cord) 164 

Sulcus  nervi  oculomotorii 53 

Sulcus  occipitalis  (es)  lateralis  (es) 13 

Sulcus  occipitalis  (es)  transversus 13 

Sulcus  occipito-parietalis 11 ,  15 

Sulcus  olfactorius 22 

Sulcus  postcentralis 12 

Sulcus  postcentralis  cerebelli 104 

Sulcus  praecentralis 11 

Sulcus  praecentralis  cerebelli 104 

Sulcus  temporalis  superior  et  medius 11 

Superficial  longitudinal  fibers  of  pons 125 

Superficial,  molecular,  or  gray  cellular  layer. Ill 

Superficial,  molecular,  or  neurogliar  layer  of  cortex 72 

Superficial  origin  of  anterior  root  of  spinal  nerves 180 

Superficial  origin  of  posterior  root  of  spinal  nerves 181 

XXXI 


INDEX. 

PAGB. 

Superior  cerebellar  artery 117 

Superior  cerebellar  veins 118 

Superior  cerebral  veins 98 

Superior  fillet. 63,  139 

Superior  fovea 151,  152,  218 

Superior  frontal  convolution  or  gyrus U 

Superior  frontal  fissure  or  sulcus 11 

Superior  lamina  of  internal  capsule 26,  53,  54,  211 

Superior  lamina  of  medullary  stem 102,  114 

Superior  longitudinal  fasciculus 93 

Superior  medullary  velum 102,  115,  120 

Superior  occipital  convolution 13 

Superior  occipital  fissure  or  sulcus 13 

Superior  olivary  nucleus 126,  216 

Superior  parietal  convolution ' 11 

Superior  peduncle  of  cerebellum 

50,  60,  64,  88,  102,  114,  115,  116,  120.  125,  150,  216 

Superior  surface«of  cerebellum 103-106 

Superior  surface  of  pons 119 

Supramarginal  convolution 12 

Surfaces  of  corpus  callosum 29 

Surfaces  of  medulla 129-133 

Surfaces  of  midbrain 52-54 

Surfaces  of  optic  thalamus 49 

Surfaces  of  pons 119-120 

Surfaces  of  spinal  cord 163 

Surcingle 37,    40 

Sustentacular  tissue  of  brain  and  cord 67 

Sylvian  fissure 10,  209,  210 

T 

Table   1 6 

Table  II 154,  156 

Table  III 207-208 

Taeniae  tectae 30 

Taenia  semicircularis 31,  35,  37,  40,  211 

Tail  of  caudate  nucleus 37 

Tangential  association  of  fibers  of  cerebrum 91 

XXXII 


INDEX. 

PAGE. 

Tapetum 94 

Tegmentum 7,  31,  40,  50,  54,  57,  65,  66,  215 

Tela  choroidea  ventriculi  quarti 6,  133 

Tela  choroidea  ventriculi  tertii 5,  44,  46,  213 

Telencephalon 205 

Temporal  lobe 13 

Temporo-pontal  tract 26,  27,     86 

Tenth  nerve 131 

Tent  of  fourth  ventricle 114,  151 

Tentorium  cerebelli 2,      9 

Terminal  nuclei  of  sensory  cranial  nerves 62,  153,  157 

Thalamencephalon 7,  205,  213,  214 

Thalamus 37,  48,  78-80 

Three  systems  of  Flechsig 89 

Third  cranial  nerve 53,  61,  124,  140 

Third  temporal  convolution 14 

Third  ventricle 31,  33,    42 

Third  ventricle  and  interbrain 42-51 

Time  of  meduUation  of  tracts  of  cord 222 

Tonsila  cerebelli 109 

Tonsil  or  amygdala  of  cerebellum 109 

Torcular  Herophili 2 

Tracing  of  impulses 185-201 

Tract  from  lateral  nucleus  to  cerebellum 116,  132,  144 

Tracts  of  antero-lateral  column 172 

Tracts  of  posterior  column  of  cord 177,  179 

Tractus  cerebro-corticopontalis,  frontalis  (see  fronto-pontal) 27 

Tractus  cerebo-corticopontalis,  temporales  (see  temporo-pontal). 

27,  85,    86 

Tractus  olfactorius 23 

Tractus  opticus 21 

Tractus  triangularis  (Helwigi) 141 

Tractus  spinalis  nervi  trigemini 125 

Transverse  fibers  of  cord 171,  172 

Transverse  fibers  of  medulla 135 

Transverse  fibers  of  pons 121,  122 

Transverse  or  basilar  sinus '    3 

Transverse  or  commissural  fibers  of  cerebrum 85.    91 

XXXIII 


INDEX. 

PAGE. 

Trapezium 121,  122 

Triangular  tract  of  Helwig 124,  141,  148,  175 

Trifacial  nerve ^ 155 

Trigone  and  area  of  Broca  (olfactory) 24 

Trigone  of  habenula 50 

Trigonum  acustici 152,  153 

Trigonum  collaterale 40 

Trigonum  habenulae 50,  79 

Trigonum  nervi  hypoglossi 152 

Trigonum  olfactorium 24 

Trigonum  vagi 152,  153 

Trigonum  ventriculi 39,  40 

Tri-radiate  or  H  shaped  fissure 22 

Trochlear  nerve  154 

Trochlear  nucleus  (pathetic) 58 

Tuber  annulare 119 

Tuber  cinereum  and  infundibulum 7,  18,  31,  44,  84,  214 

Tuberculum  anterius  thalami 50 

Tuberculum  cuneatum 147 

Tuber  valvula  and  postero-inferior  lobules 110 

Tuber  vermis 110 

Turcks'  column 174 

Types  of  neurones 68 

Typical  cortex  of  cerebrum 72 

U 

Uncinate   convolution 17 

Uncinate  fasciculus 93 

Uncrossed  (or  direct)  pyramidal  tract 138,  174 

Uncrossed  pyramidal  fibers 138 

Upper,  or  ventricular,  medulla 144 

Uvula  and  tonsils • 109 

Uvula  vermis 109 

V 

Vagus,  or  pneumogastric  nerve 130,  137,  153,  156,  157 

Vallecula  cerebelli ' 101,  107 

Vallecula  Sylvii 10,    21 

XXXIV 


INDEX. 

PAGE. 

Valley  of  cerebellum 101 

Valve  of  Vienssens 58,  64,  102,  120.  125,  150 

Varieties  of  reflex  paths 198 

Vasomotor  centers 168 

Vein  of  Galen 98 

Veins,  internal  jugular  3 

Veins,  meduUi-spinal 160,  161,  183 

Veins,   meningo-rachidian 4 

Veins  of  cerebellum 118 

Veins  of  cerebrum 98 

Veins  of  pia 6 

Veins  of  spinal  cord 183,  184 

Veins  of  striate  body 98 

Velum  interpositum 5,  9,  31,  38,  43,  46,  212,  213 

Velum  medullare,  anterius 64,  102,  115,  120,  127,  130 

Velum  medullare  posterius 101,  114 

Vena  cerebri  interna 38 

Vena  cerebri  magna  (Galeni) 2,  38,  98,    99 

Vena  cerebri  media  ; 99 

Vena  choroidea 98 

Vena  corpora  striati 98 

Venae  cerebri  inferiores 98 

Venae  cerebri  internae ^ 98 

Venae  cerebri  mediales 98 

Venae  cerebri  superiores 98 

Venae  spinales  externae 160,  161,  183 

Ventral  deep-longitudinal  fibers  of  pons 122 

Ventral  deep-transverse  fibers  of  pons 121 

Ventral  longitudinal  fibers  of  pons 122 

Ventral  surface  of  medulla 130 

Ventral  surface  of  pons 119 

Ventral  transverse  fibers  of  pons 121 

Ventral  zone  of  embryo 205,  214,  215,  217,  219,  220 

Ventricle  of  corpus  callosum 30 

Ventriculus  lateralis 34 

Ventriculus  lateralis  (pars  centralis) 35 

Ventriculus  quartus 100,  1 50 

Ventriculus  tertius 42 

XXXV 


INDEX. 

PAGE. 

Ventro-lateral  groove  of  medulla 129 

Vermis  cerebelli , 100,  101 

Vermis  inferior  cerebelli 101 

Vermis  superior  cerebelli ^ 101 

Vestibular  nuclei  of  auditory  nerve 144,  153 

Vestibulo-olivary  tract 148 

Villi  of  arachnoid 4 

Vinculum  linguae  cerebelli 105 

Visceral  centers 168 

Visual  center 71 

Visual  conduction  paths 90 

Visual  memory  center 13,  71,    93 

W 

Waldeyer's  column  of  cells 168,  169 

Wallerian  degeneration 68 

White  matter  of  brain  and  cord 67 

White  matter  of  cerebellum. 114-117 

White  matter  of  cerebrum  and  midbrain 85-94 

White  matter  of  medulla 134-146 

White  matter  of  pons : 120-125 

White  matter  of  spinal  cord 171-182 

White  matter  of  thalamus . '. , 79 

White  or  anterior  commissure  of  cord 171 

Worm  of  cerebellum 100,  101 

Z 
Zona  incerta 50 


XXXVI 


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